Econdomics.
I always wondered why people would ever buy a 3 pack of condoms. Trojans are $5.99 for the 3 pack or $2 per condom! Last month I got a 36+4 box of Lifestyles for $12. 30 cents per condom! Now that's just smart shopping. So why waste money with a 3 pack? Simple short-sightedness? They last for a couple years so even if you only need 3 right now, you might need the other 37 over the next several months. Even if you don't, give the rest to some friends.