Mild success can be explainable by skills and hard work, but wild success is usually attributable to variance and luck

Fooled by Randomness by Nassim Nicholas Taleb

The Book in Three Sentences

Randomness, chance, and luck influence our lives and our work more than we realize. Because of hindsight bias and survivorship bias, in particular, we tend to forget the many who fail, remember the few who succeed, and then create reasons and patterns for their success even though it was largely random. Mild success can be explainable by skills and hard work, but wild success is usually attributable to variance and luck.

(James Clear)

http://jamesclear.com/book-summaries/fooled-by-randomness