The water temple, when I couldn't find the next small key in the dungeon. I thought that I had used the key on the wrong door and that I was now at some kind of dead end in the game. I restarted my whole file just to find out that when i got back to the water temple that there was another small...
oh man thats it right there, the water temple gave me the most grief out of any zelda game. Once i thought i had used a small key on the wrong door and that there were no other keys... i restarted my file without ever knowing if there was a way i could have beaten the dungeon :(