user-1: I noticed recently that for some odd reason, none of my resolutions and efforts have come to fruition. My attempts to diminish junk food, social media, and other such negative behaviours have remained similar, and my attempts to meditate and exercise have lacked success. 
Q1. What could be responsible for such a lethargic and demotivated approach to training oneself? Is there a mental factor simply lacking from my practice? 
I suspect effort may be a mental concomitant necessary for improvement regardless of the insight I may have otherwise.  
Q2. Is effort, as resulting from sitting formal and consistent practice, a prerequisite for growth? Is truly effortless practice a myth?
(I ask question two because I know that some Dzogchen and Mahamudra techniques are described as effortless.)

user43: In traditional Buddhism, effort is not only the way to move forward but, almost more importantly, the main source of satisfaction! This satisfaction then serves as the main source of fuel for going forward.
The student defines a goal according to Dharma (or the Buddha / thera / guru does it for the student), the student works hard to attain that goal, the student rejoices in his or her achievement. The goal itself on every level is an increasingly closer approximation of Final Peace: first you pledge to abstain from violence, scandals, stealing, lust, intoxication etc. - and achieve that; then you pledge to abstain from thoughts associated with coarse craving and negativity and achieve that; then you pledge to learn hold your attention on one object for long stretches of time - and achieve that; then you pledge to learn to use your skill of attention control to abstain from subtle craving and negativity - and achieve that; then you pledge to use your attention to generate joy - and achieve that; then you pledge to stop clinging to any conditioned state, including joy - and achieve that; then you review your resulting state, congratulate yourself on the Final Liberation, and declare Victory.
Whereas in "formless" types of Buddhism, that very same path is re-framed in terms of the end result. So instead of setting a goal, working towards it, and congratulating ourselves on intermediate achievements - we directly jump to the non-abiding state, however imperfectly. We just say, hey, our current state is already Enlightenment and this is already Nirvana, so let's just relax in the spontaneous expression of this eternal fact. Then, if doubts about our progress and negative thinking comes up, we don't suddenly change course and jump to the traditional Buddhism with its goal-setting and effort. We don't regret that we are on the effortless path. Instead, we just look at these doubts and negative thinking, seeing them as doubts etc. - and liberate them right there on the spot, either by appealing to Emptiness, or directly. We engage into this practice in connection with various life situations until it becomes our second nature. In the process we go through basically the same stages as on the original path - we just don't think about it in the same terms.
So in essence, it is the same practice. It's just that in one case we frame it as a series of progressive realizations, connected with effort, resulting in satisfaction and a sense of achievement, until our practice gets subtle enough to defact reach non-abiding - and in the other case we're habituating ourselves to the non-abiding from the very beginning, without the intermediate vows, goals etc. and the associate sense of achievement.
In a way, the formless practice is more honest and direct, but it's also a lot more difficult psychologically, since you don't get that hero feeling you get when walking the other path. Instead, you keep losing shape, and if you encounter any obstacles including doubts, you don't apply effort to solve them brute-force, but meet them by further loss of shape.
You should clearly decide for yourself which of these paths you're on. If you are on the first path, then your thoughts about junk food, social media, formal sitting practice etc. are valid. You should clearly define success on each intermediate stage and then apply strong consistent effort to achieve that success, then review it to harness the energy. If you are on the formless path, you should drop all those thoughts about not being good enough and focus on relaxing in the self-existing perfection of your natural state. What's important is that you clearly decide which of these paths you are on.

user-1: 
Q1. What could be responsible for such a lethargic and demotivated
  approach to training oneself? Is there a mental factor simply lacking
  from my practice?

As NuWin already pointed out: habituation will play a part in this. Another factor could be the misunderstanding of the practice.
Right effort is part of the Noble Eightfold Path.

Restraining arisen unwholesome qualities. (In your case lethargy, laziness etc.)
Letting go or arisen unwholesome qualities.
Developing of wholesome qualities. (Think, f.i., of the seven factors of enlightenment.)
Sustaining arisen wholesome qualities.

So, walking the path is work. 

Q2. Is effort, as resulting from sitting formal and consistent practice, a prerequisite for growth? Is truly effortless practice a myth?

Effort is not so much a result as it is something you have to put in. And since it is part of the path it is definitely necessary. Growth can't happen without effort. 
Think of it as gardening. You can't just throw some seeds on the ground and that's it. If you want the right plants to grow you will have to keep an eye on how things develop. Get rid of weed, water the plants you want to grow and so on.
You could try to contemplate on death every day to break the habit of laziness. How would you feel at the end of your days having spent them with social media instead of meditating? Guilty? Think of the possibility of being reborn in lower reals. Stuff like that. Maybe you'll find that these reflections or others can motivate you to stick with the practice.
It will become more effortless once it is your new habit. Doesn't mean you won't put in any more energy. But your attitude towards the practice will have changed and it will no longer feel as a chore but more as a natural thing.
Hope this makes sense.

-1: <p>I noticed recently that for some odd reason, none of my resolutions and efforts have come to fruition. My attempts to diminish junk food, social media, and other such negative behaviours have remained similar, and my attempts to meditate and exercise have lacked success. </p>

<p><strong>Q1. What could be responsible for such a lethargic and demotivated approach to training oneself? Is there a mental factor simply lacking from my practice?</strong> </p>

<p>I suspect effort may be a mental concomitant necessary for improvement regardless of the insight I may have otherwise.  </p>

<p><strong>Q2. Is effort, as resulting from sitting formal and consistent practice, a prerequisite for growth? Is <em>truly</em> effortless practice a myth?</strong></p>

<p>(I ask question two because I know that some Dzogchen and Mahamudra techniques are described as effortless.)</p>
 43: <p>In traditional Buddhism, effort is not only the way to move forward but, almost more importantly, the main source of satisfaction! This satisfaction then serves as the main source of fuel for going forward.</p>

<p>The student defines a goal according to Dharma (or the Buddha / thera / guru does it for the student), the student works hard to attain that goal, the student rejoices in his or her achievement. The goal itself on every level is an increasingly closer approximation of Final Peace: first you pledge to abstain from violence, scandals, stealing, lust, intoxication etc. - and achieve that; then you pledge to abstain from thoughts associated with coarse craving and negativity and achieve that; then you pledge to learn hold your attention on one object for long stretches of time - and achieve that; then you pledge to learn to use your skill of attention control to abstain from subtle craving and negativity - and achieve that; then you pledge to use your attention to generate joy - and achieve that; then you pledge to stop clinging to any conditioned state, including joy - and achieve that; then you review your resulting state, congratulate yourself on the Final Liberation, and declare Victory.</p>

<p>Whereas in "formless" types of Buddhism, that very same path is re-framed in terms of the end result. So instead of setting a goal, working towards it, and congratulating ourselves on intermediate achievements - we directly jump to the non-abiding state, however imperfectly. We just say, hey, our current state is already Enlightenment and this is already Nirvana, so let's just relax in the spontaneous expression of this eternal fact. Then, if doubts about our progress and negative thinking comes up, we don't suddenly change course and jump to the traditional Buddhism with its goal-setting and effort. We don't regret that we are on the effortless path. Instead, we just look at these doubts and negative thinking, seeing them as doubts etc. - and liberate them right there on the spot, either by appealing to Emptiness, or directly. We engage into this practice in connection with various life situations until it becomes our second nature. In the process we go through basically the same stages as on the original path - we just don't think about it in the same terms.</p>

<p>So in essence, it is the same practice. It's just that in one case we frame it as a series of progressive realizations, connected with effort, resulting in satisfaction and a sense of achievement, until our practice gets subtle enough to defact reach non-abiding - and in the other case we're habituating ourselves to the non-abiding from the very beginning, without the intermediate vows, goals etc. and the associate sense of achievement.</p>

<p>In a way, the formless practice is more honest and direct, but it's also a lot more difficult psychologically, since you don't get that hero feeling you get when walking the other path. Instead, you keep losing shape, and if you encounter any obstacles including doubts, you don't apply effort to solve them brute-force, but meet them by further loss of shape.</p>

<p>You should clearly decide for yourself which of these paths you're on. If you are on the first path, then your thoughts about junk food, social media, formal sitting practice etc. are valid. You should clearly define success on each intermediate stage and then apply strong consistent effort to achieve that success, then review it to harness the energy. If you are on the formless path, you should drop all those thoughts about not being good enough and focus on relaxing in the self-existing perfection of your natural state. What's important is that you clearly decide which of these paths you are on.</p>
 -1: <blockquote>
  <p>Q1. What could be responsible for such a lethargic and demotivated
  approach to training oneself? Is there a mental factor simply lacking
  from my practice?</p>
</blockquote>

<p>As NuWin already pointed out: habituation will play a part in this. Another factor could be the misunderstanding of the practice.</p>

<p>Right effort is part of the Noble Eightfold Path.</p>

<ul>
<li>Restraining arisen unwholesome qualities. (In your case lethargy, laziness etc.)</li>
<li>Letting go or arisen unwholesome qualities.</li>
<li>Developing of wholesome qualities. (Think, f.i., of the seven factors of enlightenment.)</li>
<li>Sustaining arisen wholesome qualities.</li>
</ul>

<p>So, walking the path is work. </p>

<blockquote>
  <p>Q2. Is effort, as resulting from sitting formal and consistent practice, a prerequisite for growth? Is truly effortless practice a myth?</p>
</blockquote>

<p>Effort is not so much a result as it is something you have to put in. And since it is part of the path it is definitely necessary. Growth can't happen without effort. </p>

<p>Think of it as gardening. You can't just throw some seeds on the ground and that's it. If you want the right plants to grow you will have to keep an eye on how things develop. Get rid of weed, water the plants you want to grow and so on.</p>

<p>You could try to contemplate on death every day to break the habit of laziness. How would you feel at the end of your days having spent them with social media instead of meditating? Guilty? Think of the possibility of being reborn in lower reals. Stuff like that. Maybe you'll find that these reflections or others can motivate you to stick with the practice.</p>

<p>It will become more effortless once it is your new habit. Doesn't mean you won't put in any more energy. But your attitude towards the practice will have changed and it will no longer feel as a chore but more as a natural thing.</p>

<p>Hope this makes sense.</p>
