I've heard people say you should change your trainers every 6 months. I can't help but feel uneasy about this. For one it seems like marketing to me and is obviously bad environmentally. But also there's no way I could afford to do it! We're told to get the right trainers which are expensive then chuck them after 6-12 months. I've had my running trainers for 8 years and am just accepting they need replacing! I also never get injuries. What are other people's opinions on this?