Interiority? How Much Should You Show or Tell about Your Characters' Inner Lives?

Interiority or "internals" is a fancy way to describe the reader's view into your characters' thoughts, feelings, and inner lives.  Some genres require a lot of this (memoir), some much less (thrillers).  Interiority is what makes a character real to the reader.  Skilled writers reveal interiority in several ways.  It's important to know what your genre…