most important decisions are made on what street?

[Acemanhattan]

sorry for the random questions all the time, but they pop into my mind so i just write em down on paper then post a few of em. What spots do the best players make the best decisions? I know the answer would be on every street, but at what point are the "key" decisions made in the hand? Flop i imagine hand selection is key, and on the flop assessing on how or wether the hand is worth continuing with, but are these the most important spots? I find that when i get to the river if i have to make a big decision i prob made bad ones on the way there, so i am prob fuked anyways.