A tight collet prevents your router bit from slipping up or down, and ensures safer routing. But those tight collets don't loosen easily.
woodworking technique shop tip

When tightening or loosening router collets, you can gain more leverage with one hand than if you used two. Position the two wrenches so they fit within your grip. Now, squeeze the handles together to tighten or loosen the collet. This way you won't bang your knuckles together.
—From the WOOD magazine shop