Lust can corrupt just about anyone, all the more if you conjure a direct line to the Prince of Darkness and start making crazy requests. You know, like magic rejuvenation and the chance to bed every duchess in Italy.
That's the deal Faust makes with the demon Mephistopheles: unbridled debauchery and jaw-dropping magic powers all for the low, low cost of his immortal soul. See, like all humans, Faust stunk at weighing short-term pleasures against long-term pains. That's why his tale strikes such accord with the rest of us. To some extent, we all fill our days with Faustian bargains.
In some versions of the story, a repentant Faust overcomes his contract with damnation via the classic legal loophole of true love. Other storytellers send him straight to hell.
The lesson: Don't sign contracts with demonic entities, wizards, no matter how sweet the payoff seems. Credit card companies make their fortune off debt not loans, and you can be sure that hell has a similar business model.