That's a myth that no one ever actually looks into.

Truth is, we use most of our brain just not at all at once.

For instance, the happy feeling we get when doing something fun comes from a different part of the brain than the feeling of sadness that comes from the death of a loved one, so you don't use both parts at the same time.

Yes and yes. I will not go into specific details, but one of the best ways to unlock some of the potential of your brain is to develop a photographic memory. I won't explain how to do it, but here's a link for your troubles: [ Register or Signin to view external links. ]

Aaaaaandddd, this: [ Register or Signin to view external links. ]

Well it kind of is because there are separate parts too your brain that control other things like memories or remembering things so you use them in moderation or you use one that you are trying to focus on i guess if that makes any sense but yes you only use some of your brain. Study the brain or take anatomy in high school interesting class.

I'm not sure, it's a myth.
I got told we only use 20% of our brain.

No that's a myth. reporter misinterpreted what scientists said, which was that we only use 10% of our brain for cognitive function and bla bla bla while the rest is used for memory, subconscious, info and bla bla bla. The reporter only took the first part cuz hell, people will do anything for a story.

That's just how much you use

Your teacher should really do research before telling their class false information. We use more than 1 percent of the brain at a time even when we are doing nothing. (sleeping). I think it is about 5 or 10 percent. To get more, tell a story aloud that has happened to you and try to remember what happened. This activates more of the Lobes in your brain making you use more of it.

I know this because I watch Mythbusters