enter somebody's head
enter somebody's mind

Sure, it never entered my head for a moment that things weren't as they should be.

Now you've got me talking I'm thinking things that never really entered my head at the time.

That he himself should be loved was not a thought which ever entered his head.

To tell the truth, I couldn't even let these things enter my head.

It never entered his head that he was not absolutely right.

It hadn't entered her head that he would do any such thing.

"Why would it enter my head not to believe you?"

This was something which had never for a moment entered her head.

The possibility of not getting back never entered her head.

The idea that it might be someone else never seemed to enter her head.