user1853: Why did miners/pools choose the longest chain for continuing it?
Because with this strategy they have the highest expected bitcoin reward.
The expected bitcoin reward is (new generated bitcoin (b) + transaction fees (t)) * probability (p) the block will not become orphaned.
Since today b + t is clearly dominated by b and b is kind of constant, today miners maximize p by mining for the longest blockchain. But what about the days when b gets close to 0? Then, right after a completed block, b and t are 0. Thus, a clever miner should ignore the latest block, since even with a small p he will end up with a higher expected reward.
But once miners become aware of transaction fees and will not build on the longest chain this could cause serious trouble? Did I forget something or are these assumptions right?

user5406: You don't have to just find a block, but the blocks building on your block must reach a greater height than competing blockchain tips for others to reorganize their blockchain. In the easiest case that means you have to find two blocks before the whole network only finds one.
This is highly unlikely to happen, unless you have a) a significant portion of the network's hashrate at your disposal, or b) you find a block sufficiently near in time to the other block that each block reaches parts of the network first, and there are miners working on either to create a successor.

user85: I think it's conceivable that this could happen. But under realistic cases, I don't think it actually will. If you don't mine on the longest block, the probability that your block will ever be part of the longest block drops drastically. Unless a block you mine becomes part of the longest chain and stays that way, you never get any fees or reward at all.

1853: <p>Why did miners/pools choose the longest chain for continuing it?
Because with this strategy they have the highest expected bitcoin reward.
The expected bitcoin reward is <code>(new generated bitcoin (b) + transaction fees (t)) * probability (p) the block will not become orphaned</code>.</p>

<p>Since today <code>b + t</code> is clearly dominated by <code>b</code> and <code>b</code> is kind of constant, today miners maximize <code>p</code> by mining for the longest blockchain. But what about the days when <code>b</code> gets close to <code>0</code>? Then, right after a completed block, <code>b</code> and <code>t</code> are <code>0</code>. Thus, a clever miner should ignore the latest block, since even with a small <code>p</code> he will end up with a higher expected reward.</p>

<p>But once miners become aware of transaction fees and will not build on the longest chain this could cause serious trouble? Did I forget something or are these assumptions right?</p>
 5406: <p>You don't have to just find a block, but the blocks building on your block must reach a greater height than competing blockchain tips for others to reorganize their blockchain. In the easiest case that means you have to find two blocks before the whole network only finds one.</p>

<p>This is highly unlikely to happen, unless you have a) a significant portion of the network's hashrate at your disposal, or b) you find a block sufficiently near in time to the other block that each block reaches parts of the network first, and there are miners working on either to create a successor.</p>
 85: <p>I think it's conceivable that this could happen. But under realistic cases, I don't think it actually will. If you don't mine on the longest block, the probability that your block will ever be part of the longest block drops drastically. Unless a block you mine becomes part of the longest chain and stays that way, you never get any fees or reward at all.</p>
