After some really difficult firings, I now keep the badges of every associate that I fire. I keep them as a reminder of the lives that I've impacted.
They sit in my drawer and anytime I have to consider any kind of formal HR action, I pull out the badges and look through each one and ask myself if I could have done anything differently. Then, I can use that thought process to determine the best course of action with the current associate.
While some might think it is a little sick, it really helps keep me remembering the individual and how their life is impacted when losing their job.
Good luck!