Everyone has one but sometimes you can doubt it.
If you lose me, you must be crazy!
You can do me and you can don't, but the negative is the positive.
Surprisingly, I can also blow up! But no harm is done, on the contrary.
2 Answers
Nice first riddle! I think you are
mind
Everyone has one but sometimes you can doubt it.
Every person has their own mind, but you can doubt your mind i.e. be uncertain about what to do.
If you lose me, you must be crazy!
Losing your mind means to go crazy.
You can do me and you can don't, but the negative is the positive.
"I do mind" and "I don't mind" are common phrases to indicate that something someone does or says bothers you or doesn't bother you. I'm guessing the "negative is the positive" part means that "I don't mind" has a more positive connotation than "I do mind."
Surprisingly, I can also blow up! But no harm is done, on the contrary.
Something can blow your mind figuratively speaking, but no harm is done of course since having your mind blown actually means you're learning something amazing or incomprehensible.
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$\begingroup$ What is written in the second quoted part of your fourth spoiler block is often hard to translate in books, movies, etc., because for example German does not have such a "negative is positive" version of that phrase. So there it would be "positive is positive". $\endgroup$ Nov 21, 2019 at 19:10
A brain.
You can lose it, and be unsure whether or not someone else has one.