Just how common is a hernia?

Pretty much every time I've been to the doctor for an exam, I've been checked for a hernia. But the few people I've known who have had one have been VERY aware of it -- they never could have missed it. Are very minor hernias that the patients don't even notice common? Do doctors often find anything during those checks? Or is it just easy to do (i.e., it just takes a second, requires no special tools, etc) so they figure "Why not?"

Inguinal hernias are pretty common...maybe a quarter of men have them. They may not cause symptoms until they progress, and they don't always progress. But if you have one and don't know about it and it does incarcerate or strangulate, you run the risk of emergency surgery. Better to do a 10 second check and be informed.