Wait... $\textit{all}$ the numbers?!?

If we use a number line, we can see that the sum of all the positive numbers on the right are cancelled out by the sum of all the negative numbers on the left.

Thus, the sum of all real numbers is $\boxed{0}$ .

Both positive and negative numbers come under Real numbers. Now there are $n$ positive numbers and $n$ negative numbers of same magnitude and opposite in sign. So all of them cancel out leaving zero as the answer.

Ex : Let us take the sum of $-100$ to $+100$

$\implies -100-99-98-97- ......+97+98+99+100$

So, all of them cancel out expect $0$ . So the final answer is $0$ .

The same is the case with $n$ real numbers.