Quote Originally Posted by Myou View Post
But... but.... You can't stay there at all? What's the justification for that?

What if you're Tiny and can only attack by entering their square?
Justification isn't part of this thread; just the rules.
Ending Your Movement

You can’t end your movement in the same square as another creature unless it is helpless.
...
Very Small Creature

A Fine, Diminutive, or Tiny creature can move into or through an occupied square. The creature provokes attacks of opportunity when doing so.
If you're forced to use the squeezing rules you can enter, but not go through unless you render the opponent helpless while you're there. Very small creatures can go through.

The Tumble skill lets you go through and also avoid AoOs.