You'll see little bumps on the bottom in just the right places to help the egg stand upright. You can significantly increase your apparent ability by shaking the egg repeatedly before you start. You'll spread the yolk out within the egg and lower its center of gravity, making egg-balancing a relative breeze. Don't follow the common advice and hard-boil the egg. It spoils the springtime magic if you can't crack the egg after you've performed the trick.
Old myths die hard.
If you know people who still believe in the gravitational magic of the vernal equinox, then the yolk's on them.