I want you to think of a time when something came easily to you with just a basic level of effort. Did you look down on those for whom the same thing was a great struggle with recurring failure? Did you blame them for their failure?
Now think of something that eluded you. Do you blame yourself for your failure? Can you think of factors in your life beyond your control that facilitated that failure?
The lessons of failure are deep and wide, and our successes predicated upon a combination of factors. While one of those is certainly will, it is limiting to discredit the role of genetics, location, economics, opportunity, social influences and more in each of our undertakings.
Carrots, not sticks. Encouragement is more effective than judgement. Challenging should not be belittling.