You will come across obstacles in life – fair and unfair.
And you will discover, time and time again, that what matters most is not what these obstacles are but how we see them, how we react to them, and whether we keep our composure
Ryan Holiday, The Obstacle Is the Way,
Mindfulbalance 
As a student of Stoicism I’ve come across this sentiment .. and principle a couple times. I love this one as it highlights the importance of training your mind to see things properly .. that perception allows you to welcome obstacles as they bring a myriad of opportunities with them .. if you can only see them.