Alright, let's take an example. 1 is less than 2, so we can write it as 1<2. However, if we multiplied both sides by -1 without changing anything else, we get -1<-2, but -1 is greater than -2 because it is less negative, so the correct way of writing it would be -1>-2. Therefore, since a number that is less positive than another becomes less negative (and therefore higher) when both are multiplied by -1, we have to change the side of the inequality