.
1. If you have no use factor, do not use it. (It is a joke, of course. But it fits the tone of your post).
2. Imagine that you need to solve this equation
=
,
and you have no a piece of paper to write the quadratic formula.
But you can solve it mentally, by factoring the left side as (x-3)*(x-7).
Then you easily get the roots 3 and 7.
3. Now imagine that you need to solve this cubic equation
=
.
How can you do it?
Again, apply factoring and factor the left side as (x-1)*(x+1)*(x-2).
Then you easily find the roots 1, -1 and 2.