Recently encountered a tweet by Mark Suster, that reminded of the one hardest problems in life - saying NO.
Whether we’re making a product or setting life goals ; we humans inevitably tend to spread ourselves too thin. 
We want to do everything. We want a great body, a blossoming career, no too much stress, wonderful relationships and adequate sleep too! 

I fear not the man who has practiced 10,000 kicks once, but I fear the man who had practiced one kick 10,000 times  - Bruce Lee Greatness can only come by relentless pursuit and we have energy for only so many relentless pursuits. To even stand a chance of getting great at something, means we focus our time and energy on it - and to truly focus we must kill all other distractions that get in the way.