Putting "Toggle Perspective" on a mouse button doesn't change it untill i press w,a,s or d

I put the toggle perspective setting to one of my mouse buttons and it just didn't work until i pushed w,a,s,or d.

I thought it was suppose to just change my perspective with out pressing w,a,s,or d.

Step 1: Go on to a world.

Step 2: Change your perspective button onto a button on your mouse.

Step 3: Try pushing the button that you changed it to.