Trumpet Endurance problems? Mouthpiece or Embouchure?

Why do we have range and endurance issues? Is the mouthpiece to blame? The embouchure? Both?

[@idleviewer2010]

Been practicing for about 2 years now, recently I notice my lower lips curls around my bottom teeth and I get bruised inside my lip. I am trying this out but my lower lip still curls in, any advice on how to correct myself?

[@CanadianDivergent]

my lips won't even buzz today. I'm done. no one is ever just honest and says "some people's lip just are too sensitive to play the trumpet" and save them years of struggle and frustration.