There are hundreds of opinions on this. I had the same thing happen the past 2 outings for smallmouth bass. My opinion comes down to 2 things, #1 - the mood of the fish, sometimes (and this is true with trout as well) fish will "short hit", not take the entire lure, fly, etc. With streamers I feel a solid hit and lean back and come up empty, it's my belief that they are striking only the tail of the streamer, marabou on a wully bugger, and not getting the hook, taste testing if you will. I think the same about bass, they are only playing with the bait until they decide if it's food or not.
#2 - with bass and soft baits, we are usually using a single relatively large hook. Depending upon the angle of attack the fish may or may not hit the bait creating a hook turn that allows a hookup, otherwise the hook (along with the bait) simply come back out of the bass's mouth.
I have also seen while bass fishing that smaller fish, bluegill and perch will try to grab the tail of a soft plastic, which makes you think you've missed a bass.
I've debated this at great length with regards to topwater lures. The general consensus is too not set the hook immediately after you see the fish blow up on it. I've tried this tactic and will report that it makes no significant difference in my experience. I've resolved to set the hook as soon as I see or hear a splash, my theory being that at least I know the fish is around the plug, might as well set the hook while you have the chance. Other times as I've witnessed in late fall when the bass begin to get lethargic they will hit near but completely miss the lure.
