Some things I never seem to learn and continue to make the same mistake over and over. I can't be alone in this, so I figured I might start the topic and see if anyone else suffers from the same malady.
For me, the one lesson I refuse to learn is that random orbit sanders are not meant to flatten, they are meant to smooth. I don't know how many times I have used a ROS on narrow parts or sanded past the end of a board only to find out that the edges are no longer in the same plane as the middle of the part or, in sanding an end, it is no longer a right angle but an arc. All that work at the jointer, planer, table saw to keep the stock flat and square goes right out the window after only a few seconds of abuse from the ROS.
It seems the ROS, with its convenient hook and loop paper has just too soft a pad to insure that anything you sand will stay flat. Maybe someday I will learn.