You think about names, like you are expecting to name your own child. You troll through baby-name websites, look through baby name books, try to come up with weird and wonderful names, and suddenly something clicks. The name fits the character.
Sometimes, the whole character starts with a name. Oh so you are John and that's what you are like. That happens to me a lot.
What the hell do you do then when months later - when you are so used to thinking of John as John - that you realise that if you have John as a hero, you really shouldn't have Jane as your heroine? Or if you have a John, you shouldn't really have a Ron. You know what I mean. Following all those unwritten rules about making character names different.
This has happened to me a few times when either major characters have similar sounding names, or they all start with a same letter. And I always HATE changing them. Because usually by that time, I have come to think of them as people. And people (at least normal people) just don't change their names half-way through their life.
I do change them, because it will be hard enough getting published without giving your agent/publisher a reason to get confused with who is who. But still, it is annoying. And it always takes me a while to find that second perfect name that suits my characters' personality.
The way I deal with it is I decide who are the characters in question. If one of them is a lead and the second one is just some other non-major character, then no contest. The lead keeps his name. But usually (sod's law) I get two major characters with similar names. In that case, I try practicing calling them with different names as I come up with them. And whoever finds another name to suit their personality, gets a new name. Sooner or later, one of them does find a name that they like, so in the end things do work out.
How about you? How attached are you to your characters' names? How do you deal with changing them?