Sustainability – delusion or practice?

What is sustainable? Is it making a trendy decision to buy the hybrid, instead of driving your old car and trying to get the very most use of it as possible? Is it buying bamboo pants, or buying pants from the thrift store, or not shopping for new pants until you really really need them? Is it my responsibility to live up to my ideals all the time? How can I even begin? How to unwash my brain from all these years of being groomed to consume?