[Note the last paragraph] When someone is pushed to their limits, they can change. Subtly most of the time, kind of like a bend or tint to their personality. These changes tend to be temporary, although the length of time is indeterminate. It could be related to status quo that had great importance and was altered, restoring it may reverse the change quicker.
But if they are pushed beyond said limits however, expect much more than a slight alteration to their persona. Some aspects can become exaggerated to worrying levels, or may stop being detectable at all. Or they could shift an idea set entirely, not necessarily reversed though. These kind of changes rarely revert back to the original state, as the cause is mostly impossible to negate, at least from the afflicted's point of view.
The kinds of changes vary insanely, mainly on a per person basis. As each is unique both in personality and situation. But such alterations can be categorized by; tics, mentality. Tics such as a verbal tic, mentality as bias of thought like pessimist or optimist. Perhaps another but I cannot recall the third category.
Note: I am NOT a psychiatrist nor psychologist, I'm just bored enough to observe my surrounding and past events trying to find connections. Take this as a joke as you will, unless if you know any of this is true. I'm merely speculating on mental functions and what happens to them if something drastically changes. Odds are I'm shooting the shadows of ideas I don't fully understand. I am willing to discuss theories but it may take time to reply.