Question

don't spit into the wind meaning

Answer 1

Don't spit into the wind is an urban phrase widely said in the U.S, which means 'Don't do something that would defeat you or destroy you'. 

Answer 2

It means to not do something that will be pointless or harm you. Spitting in the wind means that the spit flies back into your face, it harms yourself, 
Hope this helps.