Some of these relate to culture or subculture and therefore to values, aspirations, and reference groups, but some involve situational advantages or disadvantages that are essentially matters of coincidence (for example, the predominance of professional hockey players whose birthdate guaranteed that they would be older and physically more mature than most of their cohort in youth hockey programs, which in turn meant that they would get to play more, get more attention from coaches, derive greater self-esteem from that domain, and thus practice harder and advance to higher levels of competition).