No, that's not a typo. I meant "interiority." Allow me to explain. In one sentence: it's easy to get lost in your POV character's head. Now, allow me to elaborate.
There's a natural tendency--especially when you're writing in the 1st person--to get bogged down in your character's thoughts. Now don't get me wrong. It's important to let your readers know what your characters are thinking. And inner thoughts can be extremely important to developing back story, building emotion in important scenes, etc. However, you have to make sure you're not going overboard.
I'm not saying never ever write them. There are no "nevers," no absolutes, when it comes to writing. And I encourage you to use them in your first drafts. Use any and everything that helps you get the story on paper--or the screen--in your first draft. As the saying goes, you can't edit what you haven't written yet, right? However, be careful when revising. That's all I'm saying. If you have a page and a half of a character trying to decide if she wants chocolate ice cream for dinner, there might be a problem.
I find inner thoughts become a big problem for me when the character has to make a big decision. I leave all of his or her original ruminating on the page when the reader doesn't need--or want--to know every last bit of my characters' thought processes. Just the highlights mainly. Or another writing tic of mine is to have a character express something 3 or 4 different ways through inner thoughts. Pick the best 1 or 2--preferably 1--and let go of the rest. Remember to murder your darlings. You have to make good use of that delete button during revisions.
All that to say, there is a time and a place for inner thoughts, but don't let them take over. Remember all the other aspects of good writing while your characters are ruminating: action, conflict, tension, and--whatever else you do--moving the story forward.