Something about an optimist and a pessimist. I couldn't think of a good title for this one.

Once upon a time, there was a mom and dad that had two children.
One of them was an optimist, the other a pessimist. Wanting to
understand why the two children were so different, they consulted
a psychiatrist, who set up an experiment to help figure it out.

The psychiatrist led the first child into a room that was full of
brand new toys. Immediately the child burst into tears. The
psychiatrist asked why, and the child replied, "All of these toys
are new, and if I start playing with them I'm afraid I might
break one, and then I'd get in trouble."

So the psychiatrist led the other outside to a huge pile of horse
manure. The child immediately dove in, scooping out handfuls with a huge smile on his face. The psychiatrist asked why the child was
doing that, he replied "with all this horse shit, there has
to be a pony around here somewhere, and I'm gonna find it."