There is almost always more variation within a subgroup than there is between subgroups.
The thing about this is that we often make very flawed assumptions about people based on “trends” or “tendencies.” So, for example, while it is true that the average height of males in the US is 5’9″ and females is 5’3 1/2″, there are plenty of men who are shorter than most women, and plenty of females who are taller than most males.
How often do we hear about group tendencies and leap from that to the assumption that all members of the group share that tendency?
Thanks to my friend Loyd for this thought.