It depends on the metric for success: if the metric for success is that it ends the practice you oppose, then yes clearly individual, uncoordinated action won't do that. if the metric for success is that it extricates you from having to compromise on your principles, then it's quite easy to achieve success.

e.g. Although I'd be happy for <evil firm X> to go bankrupt or desist from making the world a better place, I'd also be plenty happy knowing I'm not giving them money to make the world a better place.