The meaning of the proverb is that necessity gives rise to the invention of new things and new ideas. Man fulfills his demands in life only when he feels it is necessary and once, he feels this he finds different ways and means for it.
When we do not require anything we do not feel its need, but when we really want, we are forced to find different ways of fulfilling it. When civilization started man was totally ignorant as to how to lead a life, how to protect himself from other destructive forces.
When he felt its hire need, he invented fire to frighten the animals, so that they may run away from him seeing the fire. Art of writing was necessity for a person to communicate himself. Art of cooking was necessary for his livelihood. Gradually, as per their tastes they invented new dishes.
Necessity may be constructive as well as destructive. When it is constructive it is the desire of human beings to live luxuriously. The result is man has invented many things for his comfort, when it is destructive, it is invented out of enmity and jealously, and a desire to defeat and destroy others.
Nuclear weapon is the best example of this second type. Necessity must be
conditioned by a moral binding or inventing, only those things that help man
towards achievement of perfect happiness on earth.