certainty

As sure as eggs is eggs.

said when

Better an egg today than a hen tomorrow.

suggests that

First catch your hare.

states that

Never quit certainty for hope.

suggests that

One today is worth two tomorrows.

means that

There is many a slip between cup and lip.

suggests that

Nothing is certain but death and taxes

suggests that

Nothing is certain but the unforeseen

said to mean that

Never is a long time.

saying suggesting that