sb can (not) help (doing) sth | sb can not help but do sth
used to say that it is impossible to prevent or avoid sth :
I can't help thinking he knows more than he has told us.
She couldn't help but wonder what he was thinking.
It couldn't be helped (= there was no way of avoiding it and we must accept it) .
I always end up having an argument with her, I don't know why, I just can't help it .
I couldn't help it if the bus was late (= it wasn't my fault) .
She burst out laughing—she couldn't help herself (= couldn't stop herself) .