As many as they can beg, borrow, or steal! :)
It depends on what they've done or what's gone wrong etc. So a pedo... no chances... someone who's made the wrong decisions with their taxes or employment or relationships etc, they should get more chances providing that they are learning from their mistakes.
As many as that person can muster up to take.
As many as it takes, as long as those mistakes aren't hurting others.
To err is human, and everybody should get a fair number of chances and have also the occasion to learn properly.
That's impossible to gauge because it'd depend on the person and the issues.