Otto makes an excellent point (as usual). When I have been "solo" in Yosemite, that just means I was camping alone, not that there weren't other people about in the area at least during the day. On the other hand, I was solo hiking and bike touring in NZ years ago and for some of that time I was truly alone, so that had I gotten hurt or sick and was immobized, the likelihood of someone finding me was very remote. Not only that, but no one would have realized I was "missing" for a long time and even if they did, they would have had no idea where I was. Big difference.