Dear Xander, If change is the only constant in life, then the human capacity for learning is the one constant that will not only reinforce change, but allow us to embrace it. And the lessons we can learn can stem from the simplest and least expected situations. When you managed to stub your toe last Tuesday, your experience created not one but three lessons, learnt by not one but three different individuals. It happened at your grandmother’s house, after school and just before I came to pick you up. You were bawling — hard — in front of your dinner bowl by the time I arrived, and your grandmother felt…