I’m surprised I’ve never heard this reason before, it makes so much sense to me, and can be summed up in six simple words:
God wants you to be strong.
It must be remembered that mankind was created in God’s image. And God, of course, is strong, because He’s definitely not weak. Therefor, we must be as strong as we can in order to be pleasing in God’s eyes. The best way to become strong is through overcoming difficulties and working against resistance.
The devil, on the other hand, wants the exact opposite (obviously)! He wants us to be WEAK! He wants us to take the easiest route, be lazy, live for easily acquired pleasures. In a weak state we are EASY PREY to his manipulation!
So next time life’s tough, look to the sky, thank God, and make him proud.