[dwb]

It becomes moderately better than nothing when “everyone” (not even close to everyone) does it. And there are some decisions (taking fewer/no flights, no fossil-fueled car, etc) that are a lot more effective than others. Personally I try to do my best! But in general, individual actions are dwarfed by systems bigger than them. Even being able to shun cars is only feasible if you live in a city with good public transport, for instance.