Recently, I bought the "Rocket scientist" skill, then I duck and it doesn't do anything! I waited for a whole minute, still doesn't do anything. What should I do?

It's really weak in the beginning.
Make sure you're holding the down key down as you do it, otherwise I recommend stacking the skill a couple times to see if that resolves the issue.

I maxed it out and then I tried again. Still doesn't do anything. I'm really sure I'm holding the key, but the mouse just lays there and does nothing.

Hold down S instead and see if that helps?

Sorry, nothing... Tried both S and the arrow down and it still doesn't work...

Maybe you know this but I'll say it just to be sure: This (and all others) skill only works when you are the shaman. If you're a normal mouse it won't do anything.