John Gill Commentary Proverbs 30:21

"For three things the earth doth tremble, And for four, [which] it cannot bear:" — Proverbs 30:21 (ASV)

For three [things] the earth is disquieted
The inhabitants of it are made very uneasy; and for four [which] it cannot bear;
they are a load and burden upon it, and are intolerable to those that dwell on it, and make them very uncomfortable.