This question is partly derived from this question: Why don’t humans back up their minds when they enter the Matrix? The problem in my idea in this question was that the brain receives feelings via the connections, and it is not itself uploaded to the Matrix.
This is my idea: You usually learn that guns propel bullets at you which will probably hurt you at an early stage. But what happens if you never learned about guns, thus have no knowledge of their destructive force?
If the data from the Matrix to your brain is manipulated so that every gun could only shoot fluffy white balls which don't hurt you (according to your brain), your brain doesn't have the information to convince you that it is not normal. (Same goes for knives, swords etc.) If that is possible, you are invincible, because you see only white fluffy balls targeting you (according to the manipulated data which comes from the Matrix to your brain) or something similar for swords, and your brain is fully convinced by that, because it has never experienced anything else.
Would that be possible? If yes, why don't the humans use something like that?