As individuals, our choices make very little difference to the state of the world, often virtually none. Nonetheless, those same choices can have significant effects on ourselves, sometimes profoundly.
For example: One can give up driving for biking, and though this will make no difference to global pollution output, the profits of oil companies or the fossil-fuel focus of US imperialism, it could definitely improve your health, save you money and grant you great enjoyment of the outdoors. Or one can quit eating the flesh of domesticated animals, and though this will make no difference to the beef, pork or poultry industries or save even one cow, pig or chicken from the slaughterhouse, you will no longer be taking into your own body the products of such horrific suffering yourself, and that is bound to have a positive effect on you personally, if only at a subtle level of consciousness.
Or one can cast a vote for president believing it counts for something, and though the likelihood of your action making any kind of difference is vanishingly small, you will have succeeded in deluding yourself.
How so? In several ways: