Early in "The Bet," the banker muses that the lawyer will lose the bet because he will not cope more than "three or four years" in solitary confinement. He believes this because he is certain that "voluntary" confinement is much harder to bear than "compulsory" confinement, like a court-imposed prison sentence.
Not all of these musings, however, come true. The banker is right in his prediction that the lawyer will lose the bet but he loses by choice, not as a result of being unable to cope with the conditions of his confinement. While the lawyer did suffer from "loneliness" and "depression" in the early years of his confinement, he coped relatively well with being locked away. In fact, the lawyer only walks out five hours before the deadline and only forfeits his right to the money because he no longer values material wealth.