It happens.....
Years ago I lost a deer once and its sickening. To this day I cannot make sense of it: I had a chance for a quick hunt after school, I grabbed my bow, literally ran out to my treestand. I wasnt even there for one minute and I could see a buck coming down the trail. He stopped right and gave my a wonderful broadside and I hit him right in the chest. He ran for about 20 yards before the arrow fell out the opposite side that I hit him. When I got down there was lots of bright blood everywhere. Within 40 yards there was so much blood I decide to get my father to help me drag him out. When we both got on him at about 200 yards he worked a scrape which started to make us worry because it didn't make sense but at the same time there was good blood still. Not long after that the blood slowed then almost totally stopped and was hard to find even in the snow.
Long story short- we went for miles and did not recover that deer.