I have a dozen or so completed, some I knew the ending, but often I don't have a clue until it happens. The one I self-pubbed on Kindle was a 'no clue' until I was well over half way through. I did one chapter about the one-third point that I looked at as I was writing, decided it was junk, binned it and went off in a different direction. The MS had a few rounds of editing, but nothing significant got chopped or added. So far, out of my two glorious Amazon reviews, I've had a 4* and a 5*. The whole thing was about 120k.
Over this summer I wrote a roughly 120k sequel, complete seat of the pants, with only a beginning and a very rough idea of who ended up where for the end (mostly because I have the first 5k of the book that comes after the sequel). I had a bit of a WTF moment in the middle where I had no idea how what I had could ever possibly lead to the desired ending, wrote whatever rubbish came to mind for a chapter or two... and that fixed it. It's now done as a dirty 120k draft waiting for a first-pass edit and, so far as my very critical partner was concerned, it reads OK.
The one thing I would say is that both of these are written in 1st person, which possibly helps to keep things focused. They are also both 'crisis driven' romps, which again probably makes life easier as the story can't get bogged down too much without destroying the insane forward momentum. The second book was more challenging as there was a whole bundle of 'dodgy prophecy' and two characters inexplicably being mistaken for each other near the end, but I just seem to have the sort of head that knots all the trailing threads together on auto-pilot.
It also takes practice. There was a thread on another writing site on plotters vs pantsers, and one of the themes that came out was once you've done a few books as a pantser, the whole plot and structure thing tends to come more smoothly - like any craft, it improves with practice.
As for outlining being inevitable - if you're a pantser that's the road to hell. If you're not a pantser, go do that outline. If, as often seems to be the case, you're a bit of both, than plot and pants as the need takes you. I would strongly advise trying both, or whatever combination takes your fancy. All of my attempts to plot were disasters, but if you don't try the alternative, you don't know.
Whether plotted or pantsed, I would suggest getting feedback from a beta reader - I've written stuff I thought was great, only to have my partner tell me it's **** and give reasons, and equally I've had stuff I had doubts about and she loved it. Either way, you need some feedback that didn't start in your own head.
Finally... good luck!