From Longman Dictionary of Contemporary Englishsomebody can’t help (doing) somethingsomebody can’t help (doing) something (also somebody can’t help but do something) used to say that someone is unable to change their behaviour or feelings, or to prevent themselves from doing somethingShe couldn’t help it if she was being irrational.‘Stop biting your nails.’ ‘I can’t help it.’I can’t help the way I feel about you.Lee could not help but agree with her.somebody can’t help feeling/thinking/wondering etc somethingI can’t help feeling that there has been a mistake.I couldn’t help thinking about the past. →help
Examples from the Corpus
can’t help it• I tried not to cry but I just couldn't help it.• "Stop walking up and down like that!" "I can't help it - I'm really nervous."• He can't help it if they didn't understand what he was telling them to do.