The happy secret to better work,https://www.ted.com/talks/shawn_achor_the_happy_secret_to_better_work/transcript#t-100352

When I was seven years old and my sister was just five years old, we were playing on top of a bunk bed. 

I was two years older than my sister at the time -- I mean, I'm two years older than her now -- but at the time it meant she had to do everything that I wanted to do, and I wanted to play war. 

There are differing accounts of what actually happened that afternoon, but since my sister is not here with us today, let me tell you the true story

which is my sister's a little on the clumsy side. Somehow, without any help or push from her older brother at all, Amy disappeared off of the top of the bunk bed and landed with this crash on the floor

 I nervously peered over the side of the bed to see what had befallen my fallen sister and saw that she had landed painfully on her hands and knees on all fours on the ground. 

I was nervous because my parents had charged me with making sure that my sister and I played as safely and as quietly as possible.