can't help but
can't help but  {informal} also  {formal} cannot but  {v. phr.}
To be forced to; can only; must. 
When the streets are full of melting snow, you can't help but get your shoes wet.
When a friend gave Jim a ticket to the game, he couldn't help but go.
When a close friend dies, you cannot but feel sad.
Categories: 
 
Source: A Dictionary of American Idioms

