Before I forget, you have a typo in the title of Og Mandino's book. You said the plural form of salesman. The title is The Greatest Salesman in the World.

Anyway, I've mentioned this elsewhere, but it's worthy repeating here: fail fast.

I think I first heard this advice from Gary Halbert. He was an advertising copywriter who said to quickly drop losing projects.

That can apply to almost all areas of life. The way I think of it echoes what's been said here: the sooner you fail, the sooner you can find out what isn't working.

Another thought was what I heard from Wayne Dyer. Basically, he said that you don't fail—you produce results.

For people who like to measure things, that can be very empowering advice. You may have wanted to run 5k in X time, but if you ran it in X+1 amount of time, you haven't failed—you've produced a measureable result you can use as feedback to help you improve next time.