Most of the challenge with some stupid, high, and even impossible to be win with a small player is created by the user. Freely skip this challenge, and just waiting a normal challenge maybe from official "Rollbit".
Yes, there is no point in getting involved with theoretical impossible bet.
I have also seen crazy challenges and in addition to that there were no possible outcomes of the same.
For example, the other day the challenge was to hit the 100x with $10 wager on each roll and also you had to hit the whole thing within 10 rolls. That's just ridiculous and I am not sure what is analogy behind creation of such impossible challenges.
That's not fun, that's just grabbing your wallet and throwing it at the person creating the challenge.