"Three things are above me, four I cannot fathom ..." - the counting proverbs

Proverbs chapter 30 is full of "counting" proverbs. The verse is introduced with one number, and then continues with a higher number. Consider:

• The leech has two daughters ... three things are insatiable ... four never say "Enough!" (Proverbs 30:15)
• Three things are beyond me ... four I cannot fathom. (30:18)
• The earth shudders at three things, at four which it cannot bear (30:21)
• Three that are stately of stride, four that carry themselves well (30:29)

I think their author made a point, not just with his words but with his format as well:

If we ponder a matter, we add to our wisdom. If we ponder how many things we do not understand, we add to our humility. And while we cannot add to the word of God, we can always add to our understanding.