It takes a famous guru to make a principle out of common-sense.
Before you continue reading this post, please read this PDF document of an article written by Stephen Covey, author of '7 Habits of Highly Effective People'.
Actually, it doesn't have to be 90/10, it might as well be 80/20, or 95/5. But since "80/20" has been used for another famous principle (the Pareto's Principle, actually), Covey has to settle for another proportion.
After reading the article, ask yourself: have you been practicing what Covey has written about?
I am surprised that I actually do practice that. Really, why fuss over things that you cannot control, when you can achieve great benefits controlling things within you?
It boils down to choice.
Some time ago, someone arranged for a photoshoot session with me. On the day itself, she seemed uncontactable, but nevertheless I went to the agreed meeting place to wait for her to appear. After an hour, she didn't turn up. I left an SMS and just left the place.
Should I be infuriated? I should, but I chose not to. I'm sure many of you would be cursing at this person for her irresponsibility. She probably is, but why should I let another person's actions bother me? All I did was just head home, and get on with life. I have wasted an hour's wait, and I'm not going to waste another half a day feeling mad at her.
Life is unpredictable, but your actions can be predicted, by the mind that commands them.