A Quote from Mike Tyson

Everybody has a plan until they get punched in the mouth
— Mike Tyson

Although you probably didn't expect a deep and meaningful quote from Mike Tyson, I can't think of a better way to explain why so many plans and ventures fail.

We need to be ready for the unexpected and our plans and strategies should be designed to be flexible and adapt to unforeseen events whenever they can. We should also be on guard against  overconfidence and complacency.