Living, and doing what you think you would do.

If you continually study, there will become a time when you understand the difference between living as the "character" and "doing in the scene what you think the character would do".  This will take time to understand.  You cannot rush this; but you can always work towards it.

If in the scene you try to act the way you THINK you would or DO what you think you would in the circumstances, then you are in your own head.  If you are blocking yourself, that means you have a clear picture and expectation to live up to.  STOP questioning yourself and just live in the circumstances.  Understand what you want and go after it no matter what the obstacle may be.  You must have a want and need to chase.  DO NOT CHASE THE LINES!