When I was around age twelve I took an egg outside and, holding it horizontally (as it would rest on any flat surface) with a medium underarm thrust, let it roll off my fingers. Reaching above my head and landing nearly 10 feet away from myself before hitting the ground. Only to continue rolling (unless it encountered a large enough rock, or gravel). So, curious, I did this a few times with more intensity using the underarm pitch. Same results. Then, the curiosity that makes a child smirk took me to the second story of my home on an old balcony with zero safety features (perfect really... railing would have messed things up). After a few tries it was pretty clear that the egg would not break if it landed on normal grass, and would continue to roll. Again, the egg had to be pitched underarm, with emphasis on the rolling as you pulled your arm back and let it go to really get it spinning from 15ish feet off the ground. From there, if the path was clear, it would land about 13-17 feet away on a mostly level surface, then slowly roll to a halt. However, if in the last second of the extra 10-15 foot roll to a stop it encountered concrete or a rough surface, the egg broke like a bubble popping. While never really giving great deal of thought to why this happened.... I suppose my guess would be that the shape of the egg, the contents, and rotation would dissipate the energy something like a free runner (or Parkour runner... participant -- whichever) when he tumbles after a sprinting jump with a considerable descent/tumble landing. However if you scaled a free runners descent and landing to that of the egg it seems as though it would kill the person. With that, my guess is that the egg acts like the opposite of when vibrations from sound break glass. The shock on the surface of the rotating egg when impacting the grass seems to allow it to absorb the energy and spread it out. A kind of "bouncing back" on the surface of the shell during the initial impact and a tapering off for the initial energy as it rolls to a halt.