The big issue is the 50%, if you switch to 80% it's much less. Now if you are in the wrong side of 50% given the task was 4hours. How much additional time to 4hours you need. repeat trying to get the task done 50%*50%->25% , 50%^4 -> 6.25%. the cost of bad luck is very high.

It's it bad luck though? I would've thought that if AI can't solve it first try the probability of fixing it in second try would be higher/lower (depending on the task).