Several times, and yet the hunt still worked out.
During blackpowder season I once shot at a buck who was working a scrape. He was maybe 110 yards away, I got the gun up, eased on that trigger and waited for the boom. What I got was a "pow!" as the primer went off but failed to ignite the main charge. Hearing a misfire in the quiet woods is far louder in my mind that an actual shot. That buck whipped his head up so fast I thought he'd break his neck. My heart sank, but I kept the crosshairs on him just in case the load caught...it never did. After a minute of him scanning the woods and me having a heart attack while trying to keep the scope on him, he lowered his head back to the scrape. What?! I opened the "bolt" on my inline rifle, tipped the primer disc out to ready it for a fresh primer, and the old one dropped from the breach and hit my metal tree stand on the way down. TINK! He snapped his head up again. He KNEW something was in those Mississippi woods with him, but he just didn't want to leave that scrape. He lowered his head again and I though "Wow, I might actually pull this off." I got the fresh primer in, closed the bolt, and BOOOOOOM! He dropped face first into that scrape. Twice I thought the hunt was done and twice that bucks behavior cost him his life.
Another time I was hunting in a ladder stand with my then 5 or 6 year old son. It was getting to be sundown and while there were no deer on our field, I could see through the treeline to the next field over, and there were several doe there. I told my son to stay put while I climbed down, stalked over there, and shot one. I told him to be real quiet so we didn't spook any deer. I climbed down and began creeping. I'd made it perhaps 20 yards when I heard a loud commotion behind me that sounded like a series of blows on metal. He had dropped his hearing protection and it sounded like it hit every step on the way down. He froze, I froze, they froze. Everyone was now perfectly still, trying to either pretend like nothing happened, or figure out what just happened depending on which side you were on. After a tense few minutes I was able to resume my stalk and we put one in the freezer.
So many times it seems like a hunt is busted, but great stuff still happens. Heck, one time on public land I shimmied up a tree to hunt a power line and two guys showed up trying to do a deer drive. Ruined the whole thing. They told me to just get ready because they might push one to me. They made a bunch of racket when they showed up, and again when they left. Heck, they parked right on the field that the powerline crossed. After they left I started walking back up the powerline to the field and I heard something. It sounded like branches hitting. I stopped to look around but saw nothing. As I came up the hill and could see the field, a GIANT buck was standing there absolutely thrashing a set of small saplings. He was ripping it up not 35 yards from where those guys had parked.
The hunt is not over until you get back to the truck. Anything can happen, even when you think it can't.