don't "see" moves

I'm an advanced beginner you might say.  I've noticed that I sometimes just don't "see" or perceive options for moves.  anyone else experience that?  Is it a lack of experience, or a lack of focus, or what do you think?

It would help if you would post an example.

To practice up, I'd use the Chess Mentor and Tactics Trainer here on chess.com. They help me a lot!

Do you look at all of your checks and captures?  That would be a good start.

Also, try the exercise "what is the threat?"  On your turn, pretend it's still your opponent's turn, and ask yourself what the opponent would do.  Now defend against that (if you have no strong offensive moves of your own).