When things are in proportion, they are proportionate — their relative magnitudes are in balance and make sense the way they are. When the punishment fits the crime, it's proportionate.
Artists, designers, architects, and plastic surgeons are all people who care deeply about whether things are proportionate. After all, if you give someone a nose job and their nose turns out too small, it won't look proportionate. And that's just in the visual sense. The old adage "No use crying over spilled milk" is just a way of saying that tears aren't proportionate to such a minor accident. Tears are proportionate when you crash your car, lose your fortune, or don't get into college.