I'll give you a little example from real life experiences, but I am not going to use my numbers as for some reason, I get attacked for that.
My younger brother. This was before we became partners. His first year, I set him up with a small bankroll so he could play low stakes $5 and $10 games for experience. Not really about making money. It was part of the learning process.
So I set him up with a 10k rankroll to play red chip. I didn't track his EV precisely as I do my own or my teammates play, but for the level he was playing and the time he was putting in I estimated his EV to be roughly $800 a month. I figured his expected win for the year to be in the $8000 - $10,000 range. (maybe less with a new player making mistakes).
So to use a horseracing term, my brother gets out of the gate fast. Starts winning way above accumulated EV, for the first few months. This was actually the last thing I wanted to see happen. So after 6 months, he has won like 10 grand. That is well over the projected (accumulated EV) amount of 4-5 grand.
So he wants to start spending his winnings. I tried to tell him he can only spend accumulated EV, (better to only spend a portion of accumulated EV to allow for BR growth) but just like Alan, none of this was registering. So I let him go and spend what he wanted. Part of the learning experience.
So second half of the year, he isn't winning at all. Not losing but his second half of the year is pretty flat as tends to happen for sometimes even months at a time in blackjack. I think he won just a little bit that second half of the year. Like under $1000.
So for the total year, he had won like $11,000. Above expectation or accumulated EV, but pretty close. BUT he had spend about 13-14 thousand dollars because he spent all his winning while winning above expectation. So at years end, despite winning above "accumulated EV", his bankroll was now like $7600.
Spending winnings without knowing where you are and your winnings are in relationship to expectation, is flat out a recipe for disaster. It is almost a certainty that this will lead to your bankroll disappearing at some point. This is precisely why we track expectation and
accumulated EV is the vehicle for doing that.