Most of the poker pros are using past results to calculate their EV. In the online cash games the calc is how many big blinds are you winning per 100 hands. The tournaments are similar. How much have you paid. How much have you cashed for. Your track record is a fairly good predicter.
In a discussion before the poker boom Phil Hellmuth put his EV in poker tournaments at +600. But if you win a main event like he did and count it in the results it's going to be skewed.
Daniel Negreanu published his tournament results for 2017. He cashed for 2.792 million but had 2.874 million in buyins. So he lost 86K plus expenses that year. One of his cashes was for 936K. Without that win he would have lost big time.
https://danielnegreanu.com/year-end-results/
I remember about 25 years ago there was a tournament player on a hot streak. He was winning and placing high in tournaments for several months. Right in the middle of his hot streak I was in a cash game. He walked behind me and I overheard him ask someone to loan him $300 so he could buyin to a tournament. A few months later he disappeared from the tournament circuit never to be heard from again.
Besides having to pay juice to play in the tournaments the expenses will also eat you up.
Not long ago Negreanu said "those that make a living playing poker tournaments are as rare as birds with teeth."
A lot of the big shot players like Negreanu get their buyins paid by sponsors. Those that get the endorsements are the ones making the money.