I once had a friend who told me how relationships had been broken down by a scientist who said each person had a shield around them (invisible, of course) and this shield was their personality. He called it a Fairemont (not sure of the spelling) Shield. Basically the shield had bumps and cavities and rough spots and smooth spots. Each person had a different shield.
So how it works is, you meet people every day. Sometimes your Shields line up quickly, and sometimes your valleys, and their cavities don’t match up at all. Those are the easy ones.
The hard ones are those who, at first, appear to have the matching bumps and valleys, but the longer you know, them, the more and more the slight differences start to rub against each other. And these become more noticeable with time.
I think it’s a pretty fair assessment of the way personalities work, and have used it to describe people who I initially liked a lot, but eventually just didn’t give a crap about.