How would you go about explaining this theory to a friend?

[Python49]

I've been trying to explain to my friend the concept of a true win rate and expected value but it seems as though he's not understanding. His goal is to make $100 a day and i've explained to him that if he wants to make $100 on average he will need to play a certain # of hands per day based on his win rate. He thinks theres someway though to cheat his true long term win rate by if he gets on and plays for 30mins playing only a small amount of hands, winning the $100 and logging off. I try to explain why really based on his true win rate he didnt win that full $100 since he ran well above his win rate and that he'll still need to log the hands at some point to make what he wants to in the long run. Logging the necessary number of hands to balance out the times he runs bad and times he runs well. I just am not very good at explaining it, although I understand the concept. Can anyone else explain it better?