My hair - just a bob - had felt really heavy in the back, so I called into a hairdresser in a local mall and asked her to pop a few subtle layers in it, just to give it a bit of movement. I couldn't see what she was doing at the back and only discovered when I got home what a mess it was ... the top bit at the back was so short that it stuck up and made me look bald in one part (and I have a lot of hair, even though it's thin - that's how bad it was). Instead of slicing gentle layers into the back, she'd cut really severe step-like layers. It was bloody awful.
It took about three years to grow out. Not surprisingly, that salon didn't last long.