Twilight messed up big time, and as a result she is paying the price when vengeful ponies trap her and Spike in a situation where they are doomed to perish if help does not arrive on time.

Lessons:

-Make sure you know what you're doing before you decide to help someone.
-Beware of your serious mistakes, for they can come back to get you.
-Honor and fighting for it is not always the smartest thing
-Some people cannot be persuaded to change their minds