that once you found out you felt like an idiot  

Its those moments were you are scatching your head and saying "Where do i go" or "what do i do" and then you discover it something completely obvious and you feel like an idiot.

I will start  

When playing portal and finishing the final challenge i escape the flames (i knew that part) but once i got on the concrete part i didn't know what to do, and glados said wait there for someone will come for you. So i waited thinking that something will come and i would take it down. But really what you were suppose to do was look up and launch a portal and escape. I felt like an idiot for standing around waiting. 

post yours 

All three metroid primes!

i did the same thing actually.

but ,if you want to include real life, i always like to get lost, its too much funner for me >_>; , also to me its the best way to learn the road.

Metal Gear Solid.

Yeah I was 6 when I first played it and I got lost so many times it's ridiculous.

Well back in the PS1 days, I picked up both Saga Frontier and Final Fantasy Tactics at the same time. I played Saga Frontier first, got totally lost, had no idea what to do, got really frustrated! (it really was a confusing game!). I ended up putting it down then playing FFT and playing that for 100 hrs. I don't think I ever played Saga Frontier again... :-O

In other news, I just bought a Saga 2 special edition DSi (which includes Saga 2 aka Final Fantasy Legend 2) with it. ;-p

http://www.siliconera.com/2009/07/22/heres-the-limited-edition-saga-dsi/

Water Temple in OOT, now I can school it in 40 min flat.

Ditto.

Also in Half Life 2 on "Highway 17" a section asks you to find two car batteries to power up a gate switch to open the gate. One was already in the socket. The second was in the bathroom of the house. And the third was in a car south of the house. It took me 20 minutes to find the last one.

Final Fantasy VII. In disc 2 when your in the snowy area near the Northen crater. I beat the boss but for some reason Cloud wouldn't climb up the crater so I assumed I'd missed something. I went back a forth multiple times until I finally realised Cloud COULD climb up the crater, you just had to be a bit more specific in the direction... leveled up a lot though :D

In Final Fantasy IX, at Terra, I had no idea how to get those treasure chests littered around in the room with all the teleporters. I walked around for 20 minutes trying to find out. Then  I fucking figured out why some teleporters were red. They were different entrances. I hit myself hard on the forehead.

Not being able to get past the icy cave in pokemon gold for 6 months. A friend did it in like 30 seconds and i was grateful.