I don't think I've ever encountered a part of a road or trail that was truly 'impassable'; where there's a will, there's a way and I absolutely despise turning around (I think it's an OCD trait), thus having a tendency to put myself and others through heck for the sake of continuing. The only exception I can think of was the AZ trip I took Scott and John on a couple of years ago, but I'll get to that in a minute...
Back in '01 I took a trip to Baja, and we decided to take a side trip to an old Spanish mission out in the middle of nowhere, near the bottom of Baja Norte. The map we had showed a trail going to it, then continuing past it, returning to the main route. It was a long and very tough trail with a lot of descents, but gravity worked in our favor and we didn't give it much thought because we weren't going to have to come back that way... well, the trail eventually ended at the mission, and I mean
ended; we hiked around for a while trying to find anything that so much as resembled a trail, with nothing but shear cliffs etc
. There was no way we were going to get out that day, so we camped at the mission, then got up early to fight our way back the way we came. It didn't help that we were out of water either. Pictures never do justice, but this hill (which came immediately after a very tough, deep swamp) was very steep and off-camber (in the wrong direction too), with a tight bend to the right about 1/2 way up. The boulders were basketball to beachball sized, and for some reason I refused to unload my XR
We finally got the bikes up it, and the rest of the 15+ mile trail seemed so easy
. After returning home I decided to research the old mission, discovering that it was nicknamed "
Mission Impossible"
The only time I can think of that stopped me (sort of) was the AZ trip in '07. It was the 1st day of the trip, and the river was very swollen. We'd ridden all day (another story) and I had no intention of turning back, but the crossing, while possibly doable, was flowing fast, and if it pushed just one of us over, the trip would be over for all of us on the 1st day.
The "crossing" (Photo courtesy of Scott):
The 4wd quad had just crossed, but not without some tense moments... so we went up-river
Doesn't look like we'll make it across here either
But like I said, where there's a will, there's a way