I am sure like me you have read than you should learn to say NO to others in order to increase our productivity. It's a good idea, but not enough.
In my opinion, there are more than one NO that we should learn, actually there is a NO that we should avoid, a NO that we should learn to use and the NO we need to learn to use.
We don't know how to use the word NO appropriately with ourselves nor with others; the result is that we say more NO's when we should said “YES” and more “YES” when we should had say “NO”. Only when you learn to use NO appropriately to yourself, you will be able to apply it to others.
My intention is to show you that there is not a unique NO, your adventure will be to use them properly.