I've only had few LDs, and most of them are very short (I always get too excited when I realize that I'm dreaming).

But one thing that bothers me is, even though sometimes I discover that I'm dreaming, and I know %100 that this is a dream .. but I can't do anything unnatural!

The finger-thought-palm test only worked once .. even though I tried it in like 3 or 4 LDs.
I mean, I know for sure that this is a dream, and I want to do things, but they just don't happen! I don't think that I was being in doubt or anything ..

What are some possible reasons?
is it because I'm getting excited?