Beggars can't be choosers. If you can't stand the heat, get out of the kitchen. Make hay while the sun shines. Don't cry over spilt milk. Don't put the cart before the horse.
Necessity is the mother of invention.
No pain, no gain. The squeaking wheel gets the oil. A leopard cannot change his spots. You can lead a horse to water, but you cannot make him drink. Barking dogs seldom bite.