Keeping visual contact with a critter being tamed is essential until one sees the taming acclimatization icons emanating from the creature being tamed. Losing visual contact with a wolf being tamed before this happens or the new day dawns can lead it to despawn.

I had once captured a 2 star wolf in a mountainside taming pit when I was attacked by a fenrig. I was attacked in the evening by a pack of 3 wolves, one of which was a 2 star. I ran toward my taming pit, killing the normal wolves along the way, having not succeeded but tried this before, I died in the process (from taking too much damage from too many wolves), the 2 star wolf was my focus. I was probably only 3-5 metres away from the wolf, which was still slightly agitated and had not yet eaten the food dropped in the pit. Not wanting to lose visual contact with the wolf I waited until the last second until the fenrig came to me and attack. When it was close enough, I took a step or 2 towards it and hit it twice with my porcupine killing it. When I looked back to my taming pit and the 2* wolf but the pit was empty and the wolf was gone, despawned. Moments after that the game music declared a new day had dawned, along with the day number onscreen. Having never had a creature despawn while taming, I must admit how ticked off I was at how quickly and easily the wolf despawned. I literally just lost visual for a few seconds while standing so close to it but the fact that this all happened on the cusp of a new day dawning made sense, in that I did not have visual contact with the wolf, and it had not yet begun to acclimatize at the dawn of a new day.