Critical Moments in Chess!?-?!-?!?

I need help with something. I am 2300. I know what a critical moment in chess looks like. I want to know, how would you define one based on elements of a chess position.

off the top of my head, this is what I could think of, am I missing something??

Thank you so much.

1. pawn moves (they cant move backwards, and they are not really key developing moves)
2. exchanges (exchanges win time, or tempos, but they are also like pawn moves, they cannot be taken back)
3. opening selection!? !? ( the opening you choose is a critical moment)

Thanks!!....

hmmm... would have been nice to have the input of the team, thanks.

I know, he  has two good books, imagination in chess, and the other one. they are great

lack of retractability. thanks. in real like i was hoping for more. i remember picking up a book not too long and it had this phase explained well. i need to look for it again.