Or on a fail, the same charter tries again:
"I pick the lock" (roll.)
"You are not successful."
"I try again" (roll).
I never understood this solution. This basically means each and every player can just keep rolling until they hit 20 (wether or not regarded as critical, per DM). Or, don't roll at all and always take 20.
I don't allow retries unless something happnes that dramatically changes the situation. To me, the roll assumes the character is already doing it to the best of their abilities - making the retry moot - and the number that comes up is the cumulative sum of unseen factors, star alignment, and other voodoo of your choice.