FWIW, both of my girls belonged to our school's chess club at some point. Their coach couldn't understand their erratic performance. DD12, in particular, was the only kid who beat the kid who won the tournament but she would lose to less competant players. When I talked to DD about why she thought that she played better against some players than others. She told me that she played better against people she liked because she wanted to spend more time with them. Against the "annoying boys" and one of the girls that she didn't like, she lost as quickly as she could so she wouldn't have to be with them. DD14 then fessed up that she used to do the same thing.