1. Assume self-interest on the part of (many but not all) other people. 2. See if you can convince some other person to give you money to solve a problem, wher

1. Assume self-interest on the part of (many but not all) other people. 2. See if you can convince some other person to give you money to solve a problem, where your solution involves something besides or in addition to physical labor. (Many but not all jobs qualify.) 3. Success? Congratulations, you are very likely not retarded. 3b. Not convinced because of the "many-but-not-all" qualification? Keep repeating 2 until you are. 3c. I admit that this will never refute the idea that every other person in the the entire world is conspiring to make you feel normal in spite of your deficiencies. (And now I'm part of the Conspiracy.) This seem identical to me to the problem of solipsism, so it doesn't bother me to not have a good answer for that.