While I acknowledge the original point, I think that the question "are you 100% self sufficient" isn't the optimal one to ask.

I suggest that no backpacker is ever 100% self sufficient --- I could never carry enough to be 100% prepared for anything. It's always some sort of grey-scale judgement of what to take to be warm, dry, fed, safe, etc while not carrying too much weight. And of course that being prepared is about more than just the gear carried.

Some gear is needed of course (!), but more important IMO is the knowledge, experience, and wisdom/prudence to make the best use of that gear and in general to make good decisions.

For my part, I don't depend on others as backup (whether hiking solo or in a group). On well-traveled trails, however, I appreciate that I'm a little safer just because others are more likely to come along (and I, in turn, enhance their safety net in the same way just by being out there).