What causes most challenge failures?

What do you think is the biggest reason traders fail prop firm challenges?

Is it poor strategy, oversizing, revenge trading, breaking daily loss limits, or changing a strategy after a few losses?

I think this is worth discussing because the solution depends on the actual problem. A trader with a good strategy but poor discipline needs a different fix from someone whose strategy has no tested edge.

What has been the biggest lesson you've learned about managing risk in a challenge?