Why 72%?

11 is in the ground family (2, 4, 8) and 3 is in the heart family (3, 6, 9). 11 is a master number, so it is matched as its root, 2. Ground with heart starts at 70. The nudge comes from the roots: 2 + 3 = 5, which leaves 2 when divided by 3, so the nudge is +2. 70 + 2 = 72.

Out of the 78 possible pairings, 43 score higher than this one. Rarity: 6.5% of birthdays from 1950 to 2009 give 11 and 11.1% give 3, so about 1 in 69 random pairs of birthdays land on exactly this pair.

The rule is our own design, not a numerologist's chart, and numerology is not a science.