10 yds and NoGo?? Assuming that you used your 1st sight pin, and assuming it's setup for 20yds... it's certainly possible that if you didn't aim a little lower than you thought you needed to, that perhaps the arrow sail over his back? Did he "duck the string" by trying to duck down last second and that's perhaps why it missed? (Doubt that at 10yd)
RE: tips... when on your sit... in the beginning of the morning... look around your FOV.. anyplace you think it's likely you might end up having a shot opportunity within that FOV... you need to range-find all the nearby objects to all those spots... then... throughout the day.... when you look at each object, say back to yourself it's range, and say back to yourself on or between which two pins you must hold if your target was to appear at that spot in the FOV.
Much like you I found out the painfully hard way that being off even by even 5yds on your range estimation, versus which pin placement you elected to use in that moment... can result in that arrow shooting under the buck or over the buck.
Also... if where they stand ends up being in front of some vegetation that "looks" like the arrow could probably drill thru it and get em? Nope... chances are likely that ain't gonna happen. Spend some time ahead of time clearing away problematic areas you spot when at your sit spot, whether that's tree or ground.
Other than that... just things like after you're drawn back, point the fingers on your hand holding the bow forward such that you you cannot impart any kind of torque'ing movements upon the bow with your gripping hand. And.. make sure it's a clean crisp release, seated and tucked in tightly to cheek/jaw, otherwise it can be possible to impart some tiny amount of side-to-side upset during releasing.
Yeah man.. definitely been there.... and you find yourself SCREAMING curse words in silence as this amazing animal rapidly slips away. Depends though, if you hold and don't move... lotta tiomes if you wait long enough, they just might calm back down and allow you to take another shot! That part, to me, is magical about bow, that's it's even possible to try again without them running away.