"Don't spit in the wind" is a commonly euphemized phrase in the USA, out of "Don't piss in the wind," a British nautical phrase with a literal meaning. Both phrases mean "Don't do something self-defeating," in the sense of "If you try to expectorate (urinate), don't do it into (against) the wind or the saliva (urine) will blow back on you in a nasty way."

A futile act is "spitting in the wind." So is a selfless but unheeding act that "boomerangs" or has dire consequences the doer hadn't contemplated, an act that "did more harm than good."

When you eat dirt for the first time and leave your family to build a shack in the woods