When we multiply a vector by a scalar number, each dimension of the vector will be multiplied by the number.
For example, multiplying the vector <3, 4> by 2 would create the vector <6, 8>.
But if this scalar is negative, the dimensions of the vector will change the signal:
vector <3, 4> multiplied by -2 creates the vector <-6, -8>.
This causes the original vector to change its direction to the opposite direction, that is, it flips 180°: