When to let things let go and when to fight for them? I find myself in conflict with the Buddhist idea of letting go.

If someone insults you, is rude to you, insults a loved one, harrases you or a loved one and so on. According to Buddhism, we should forget about it. Past is past.

But then on the other hand Buddhism also mentions that we should be courageous. And sometimes being courageous can lead to further pain. Say that you confront people who insult a loved one and then they stab you.

I'm having a problem to decide when to confront and when not to.

For now, I always let go and I feel like a doormat sometimes.

Thank you.
I think the best message on this topic is the Akkosa Sutta: Insult (SN 7.2) -- about insult and anger:

The first message is that, in order to not accept an insult, don't (violently) reject it, just don't participate in it

And secondly,


  You make things worse
  when you flare up
  at someone who's angry.
  Whoever doesn't flare up
  at someone who's angry
      wins a battle
      hard to win.


For what it's worth I think that my "martial arts" teacher taught just about exactly that same message -- about anger, fighting, and so on.