Everyone is running around trying to satisfy desires and avoid pain. But satisfying desires only results in momentary pleasure, and avoiding pain only results in temporary relief. There are always more desires to chase and pains to avoid, and so our lives consist of constant agitation and little lasting happiness or fulfillment.
The reason for this is that nothing in the world lasts. Everything is in constant change. So, no-thing can completely satisfy or give continual relief. That can only come from something constant.
But our deeper nature, call it soul or Self, is constant. Not only is it constant, but its nature is joyful.
So, to find lasting fulfillment, seek the Self. Yoga is a time-tested path to do so.