It is the relationship itself that reflects the qualities of the person. And that often requires people with specific attributes. In real life, I suspect we are surrounded by those special people. Situations can be changed with ease. I put the character in whatever kind of situation I think will make an interesting challenge and make a good story.
Situations show the length and breadth of the character's motivation.
But there are certain kinds of jobs that the character would do, and certain kinds that he wouldn't. The thing that a character has choice a over and really reflects his character is his job. The job is in some ways a portrait of the person. His job reflects a little of what his life is about. So, there are three aspects of a person's life that can be distilled from this that really reveal the character.