It's a conversation that no leader wants to have with an employee. First of all, it's hard to come out of such a meeting without having made an enemy. More than that, though, you've spent all this time, money, and energy training a person only to have to end up letting them go. It just seems like such a waste. Can anything good ever come out of terminating an employee?
When you have to let someone go, I think the important thing to remember is what the impact with be on the rest of the team. Of course, you want to try to keep people and provide them with better training to develop them into great assets. But you can only try for so long before a bad employee becomes too much of a burden on your team. Always ask yourself, will the team be made better or worse by letting this person go? That question, more than any, can help you decide if it's the right thing to do.
One other thing to keep in mind is that firing an employee might just be the best thing that ever happened to them. Perhaps the employee needs the wake up call to straighten out his or priorities. Or, perhaps it's simply that they're in the wrong line of work and you are freeing them up to find greener pastures. Who knows? They might even come back at some point down the road to thank you. You just never know.