Ouch. That is something that can hurt your brain, but actually mathematicians have a ton of tricks up their sleeves. Remember the number i, which is the square root of -1, a thing that would not normally exist if there weren’t a category of complex numbers used in math?
In the same way, the sum of all positive ie natural numbers is a divergent sum, something that does not lead to a straight point, instead it leads to infinity. In any case, as with complex numbers, the mathematicians came to a conclusion that if they were to put a number of this infinite sum, what would it be and it turns out that -1/12 is a solution that shows up quite often when trying to calculate this sum.
Math can be really crazy, that is for sure.