Normal Vector in the place

Question

I've seen two definitions of a normal vector to a curve in $\mathbb{R^2}$. Suppose we have a parametrisation of our curve: $r(t)=(x(t),y(t)),$ Then differentiating once gives us a tangent vector, differentiating again gives us a normal vector. Also $(y'(t),-x'(t))$ is normal, but I don't see how these two vectors always point in same (or opposite) direction (since we're only in $\mathbb{R^2}$).