Characters in company

I came across this gem while reading Peter Cameron's The Weekend. Although it says something to me about getting to know people in real life, it's also food for thought when it comes to building fictional characters:

"It was strange to see someone you have only known alone begin interacting with other people, for that somebody known to you disappears and is replaced by a different, more complex, person. You watch him revolve in this new company, revealing new facets, and there is nothing you can do but hope you like these other sides as much as you like the side that seemed whole when it faced only you."