That's an easy one.
Picture it...14 years old...opening day...first day with dad's lever action 30-30...a one sider comes trotting right over the hill quartering toward me. I don't stop him to and proceed to unload on him in about 30 seconds flat. BUCK FEVER!!! Instead of waiting on him to expire, I hoofed it after him. Found him sitting up 50 yards away. Reloaded my remaining 4 shells. He took off, and four shots later he's still running. Is there a blood trail? Oh yeah. Dark, dark gut-shot blood. So, I'm out of shells. I go back to the truck, get out my single shot 16 gauge and get back on the trail. I track the buck another 100 yards, find him sitting up again, and finally, finally close the deal. What a mess!!!
Needless to say, when you put yourself and an animal through something like that, you learn a ton. I'm proud to say, though, that since that day 23 years ago, all of my deer have been one-shot kills.