I have been fortunate and I take credit for some of it due to what you said - PLAN - I was taught very early that with a pencil and paper you can do anything - it is true.
That's because pencil and paper seem so basic now.
But back in the days of the ancient Greek philosophers, they thought it was a disreputable crutch to have to write something down to calculate it. They thought you should be able to do it in your head.