“Difficult but possible is the key. That’s because more difficult goals cause you to, often unconsciously, increase your effort, focus, and commitment to the goal; persist longer; and make better use of the most effective strategies.” 

― Heidi Grant Halvorson, Succeed: How We Can Reach Our Goals

This quote is a common theme and way of thinking that I completely buy into and how I live my life.  This is also how I raise my children.  I teach them about challenging themselves.  I teach them that give full effort to things.  To continually practice and work hard to improve.  I also model this in my life as best as I can.  Persist longer.