A hundred years ago — and that's when this picture was taken, in 1912 — men didn't leave home without a hat. Boys wore caps. This is a socialist political rally in Union Square in Manhattan. There may be a bare head or two in this crowd, but I think those heads are women's.
Here's another rally, Union Square again. This time it's an Occupy Wall Street demonstration. A hundred years have passed. Same place. Same kind of crowd. But this time: hardly a hat.
Hank Aaron breaks Babe Ruth's record for career home runs as he hits No. 715 at Atlanta-Fulton County Stadium on April 8, 1974, on his way to a career 755 home runs. Research suggests that in a wide variety of professions, including collegiate and professional sports, a small but significant number of individuals perform exceedingly well and the rest of individuals' performance trails off.
For decades, teachers, managers and parents have assumed that the performance of students and employees fits what's known as the bell curve — in most activities, we expect a few people to be very good, a few people to be very bad and most people to be average.
The bell curve powerfully shapes how we think of human performance: If lots of students or employees happen to show up as extreme outliers — they're either very good or very bad — we assume they must represent a skewed sample, because only a few people in a truly random sample are supposed to be outliers.