What are the three things that can never be satisfied?

This comes from Proverbs 30:15-16

15 The leech has two daughters:
Give and Give.
Three things are never satisfied;
four never say, “Enough”:

16 Sheol, the barren womb,
the land never satisfied with water,
and the fire that never says, “Enough.”

The use of three … four is typical Hebrew idiom and the second number is intended. Other examples of this are Proverbs 30:18-19,29-31; Amos 1:3.

So there are actually four things that can never be satisfied and they are listed in v16:

1. Sheol (the grave)
2. the barren womb
3. the land never satisfied with water
4. fire.

The passage is a warning against greed. These four things are never satisfied, and we need to be careful that we are not greedy and also never satisfied.