Medical doctor who tried science now wants to quit Phd and science altogether. How to explain to supervisor? I am a medical doctor, but decided to go into a graduate program because I wanted to contribute to progress of humanity with new knowledge ( I know, very romantic).  I got accepted into a graduate program in Germany (I am not German). 

Now that I am in science, I have realized it is not what I expected. Getting a job in academia is very VERY hard ( particularly in Germany I think), the life of a professor is not what better suits the lifestyle I want to lead in the future,  and a job in the industry is not really what I want, particularly having the possibility of doing a medical residency and having my own practice one day. 

I have already finished my masters and thought I could do my PhD and use the 3 years to learn the medical german language and later apply for a medical residency here.  But as time goes by I am forgetting everything I learned in med school and I cannot focus on learning German while doing a PhD because of all the work that comes with it, of course. 

Don´t get me wrong, I like my PhD project, the lab and doing research per se. It is just that I feel these would be years dedicated to something that I do not want to do for a living. 

So... 

I have not share any of these thought with my PI, so, how do I tell him that now all of a sudden and without previous notice, I don´t want to do the PhD AT ALL, especially after having shown enthusiasm for the PhD in the past ( just a couple of weeks ago!)?  That is, without looking like I was faking enthusiasm/ was just „using“ them. 

Additionally, I am in the 4th month of a one year contract. I would actually like to work the remaining 8 months to get all of my work in order to hand it over. However, is it possible by law that he "fires" me and does not allow me to finish the one year contract?
There is no problem here. Just inform the PI that you intend to leave the program at the earliest opportunity. You haven't signed a contract with the devil for your soul. People change, people grow, people learn. Others understand that. 

It would be good, however, for  you to do what you can to leave things tidy when you go, not leaving others (PI, other students) in the lurch. To do this effectively you may need to spend some time cleaning up the current work and either finalizing it or passing it on to another. That is courtesy, but useful to you for the future if you decide later to re-evaluate yet again. 

Take care of yourself; your future is yours and yours alone.