My trek last Saturday got me to thinking about this. Know when it's time to call it a day. This time, it was because I was getting cold, but I've also had that thought when it's been too hot to be out, when I've been tired, when I've walked too far, or I'm just feeling less than optimal. Go out, but look out for yourself. There will always be shots that you won't get. Trashing yourself won't change that.