Exactly, wheelloon - so before you beat yourself up too much (and have others join in on the fun) -
a) every inventor thinks they have the greatest idea since sliced bread. Ideas are like children - no matter how ugly they are to the neighbors, we always think they're beautiful. We invest emotions into them, and when they come up against the cold world of facts and statistics, we get a brutal awakening. It seems harsh, but you can't ask for reviews and not get impartial opinions that burst bubbles.
b) Bro. Owen said the same thing a bit ago - there have been so many ideas, twists, spin offs and the like that it will be tough to come up with things that haven't been done in times past. Even a neat book like The EOTVGS doesn't always tell you every game mechanic or related details ever used before, so welcome to the crowd of us who thought we had a great idea for a 1980s style game and found out later it had already been done in 1953 - or maybe even earlier on radio. The old pros weren't dummies - they were clever, too.
