I've only been at this not quite a year but here are a few of mine so far...
My 1st was one I headed out to find that took me to the middle of a gravel parking lot with nothing around. Embarassed to say even checked a few larger rock in this lot while scratching my head. Come to find out I needed to research what a chirp cache was...
My 2nd epic fail...was loding several caches into my gps, going to one and not finding, going to it a 2nd time not finding, trying again a 3rd time only to find out it didn't exist anymore (last time with new people I was showing geocaching to). No wonder I couldn't find it! Note to self: always update gps before heading out...
Oh, not a failure but I got my 1st tick in my 36 years of life when I started geocaching. Let me tell you, I'm a woman that doesn't deal well with bugs, let alone bugs that don't want to let go!!!