One of the lessons I learned last week at Stanford is that:

(Realized performance) = (Skills) + (Luck)

And therefore our expectations are always distorted as follows:

(Expected Return) = (True Expected Return) + (Random Error)

Here is an outstanding article about Luck, Creativity & Success by Ted Karczewski

http://www.fastcompany.com/3047018/how-to-be-a-success-at-everything/how-the-most-successful-creatives-create-their-own-luck