The Hammers had a 2-1 lead when Sunderland ace Kenwyne Jones was sent off in the first-half.
But Kieran Richardson managed to save a draw for the Black Cats.
“It’s encouraging the way we came forward but we have to become a little bit more mature because it’s situations like that we have to control,” Zola told Sky Sports.
“I’m trying to find an explanation because we were in total control of the game and we let them come back into the game.
“I can’t understand really. I’m upset because we are in a position in which, for the way we play, sometimes is unbelievable.
“But if you play the first-half like that and then you play the second-half with some problems if has to be solved because I can’t live with that.
“I’m really, really, upset.”
