There exists a relationship between the size of one’s index finger and the size of one’s nostrils. More clearly, I believe the diameter of the index finger and the nostril are so that the owner’s finger is the perfect size for picking his nostril without going in too far. A person with larger fingers will have larger nostrils or perhaps larger nostrils beget larger fingers? I’m not sure which one is the instigator or if they both sort of grow with the body keeping them in check. 

So, I can safely pick my nose or not-so-safely pick any nose larger than mine, but none of my fingers can pick my son’s boogery nose. I’m sure one day I’ll wish he didn’t pick his nose, but right now, I wish he could.