We all know that i doesn’t have any sign: it is neither positive nor negative. Then how can people use −i for anything?
Also, we define i a number such that i2=−1. But it can also be seen that (−i)2=−1. Then in what way is −i different from i? If it isn’t, then why do we even have something like a −i?
The vector (1,−2) is also neither positive nor negative, yet there is value in having the operation −(1,−2)=(−1,2).
Note: there is no natural meaning for “positive” for vectors, this is just an analogy.