The original question had to be edited. I would suggest that Andy's characterization shows solitary to be hardly a hardship because of his makeup. By definition, Andy is alone, aloof, and reflective. This becomes confirmed when Andy recognizes that this condition is what drove his wife into the arms of another man. Andy's nature is not to move closer to people. Andy is much more comfortable with finances and projects, as opposed to human beings. His first couple of years at Shawshank are spent alone and in a type of solitary confinement in terms of his relationship with other inmates.
It is for this reason that solitary was not something that was beyond his capacity. Being alone and independent from others was Andy's state of being, in general. Solitary confinement could not break Andy because of this. Andy was never dependent on the social attachments of others. For this reason, he is able to endure solitary in a manner that does not wither his resolve. If anything, it strengthens it because it gives him an opportunity to reflect and think, elements that he embodies already as part of his characterization.