It doesn't work for everyone.

Once upon a time I tried to add fiber into my diet. I started with fruits, vegetables, high-fiber cereals. All was going well for a while into the diarrhea started. It lasted for DAYS. Do you know what it's like, to have wiped your ass so much that it is so tender and bloody that you can no longer sit down? Do you know what it's like to try wiping yourself without actually touching your own ass? Fiber, never again.