Then my sister sidled up to me. Several people had asked, she reported, her eyes not meeting mine, whether the character of Neil was based on her husband. I was astounded: as far as I was concerned the two couldn't have been further apart. I couldn't see why anyone would think that. Well, she replied. There's the moustache. And the job. And the ex-pat angle. And the reading computer manuals in bed (which I naturally didn't know about). And... I was so embarrassed because the points of similarity were there but honestly, it had never occurred to me before.
And I've just done it again. Kissing Mr Wrong has as its main male character a WWI expert called Nick. And my son is a WWI expert called...Nick. My only excuse is that I think it's a nice name and apologies to my son...but if he's divorced with two children, then as his mother I really should know about it. I suppose that's the answer - you give 100 characteristics to a character, and the chances are some of them are going to coincide with those of a member of your family and friends. Still. It is embarrassing. Sorry Nick.