Use this phrase to talk about something that you can't control.
A common word to follow "can't help but" is "wonder". This expresses something that really makes you curious:
I can't help but wonder what my life would have been like if I'd gone to college in the U.S.
When you use this phrase in the past tense, "notice" or "overhear" are common. They're a way to start a conversation with someone:
I couldn't help but notice that your t-shirt has some Korean writing on it. Do you know what it says?
I couldn't help but overhear you saying something about a film festival. Are you a filmmaker?