"Isn't it dangerous?"
"Don't you get lonely?"
"What if something goes wrong?"
The list goes on against solo traveling. Many people have never done a trip alone for longer than a day or two. Even fewer have done it in a foreign country. Some never will.
I hadn't done a trip longer than a few days before Vietnam. Now, I am writing this on a beach in Nha Trang, having reached the end of my trip. Over these two weeks, I've learned a lot. When you travel solo, it's a completely different experience.
Is it dangerous? Yeah, if you're stupid, but the same is true of any activity. I would argue that it is more dangerous to travel in a small group--you stand out more as tourists and become more likely to be a target of a scam or a bag snatching. If you're by yourself, as long as you hide your Lonely Planet, learn a few phrases, and respect local customs, locals may mistake you for one of them. After I got a Vietnamese haircut to blend in better, I paid local prices at attractions when I asked for a ticket, "Cho toi mot ve." Even if you don't blend in as well (apparently I look Vietnamese), you may be at least mistaken for an expat.
Do I get lonely? Sure, at times. Christmas alone could have been rough. When you travel solo, though, you become more outgoing. You have to talk to people. There are some travelers who like to stay in and read or whatever. A little bit of that is okay, but it gets boring pretty quick. And when you're bored and by yourself, that's when you get lonely.
On Christmas Day, I took a walking tour in Hanoi. Once finished, my tour guides mentioned that they were university students. Our tour ended next to their campus and they asked if I wanted to see it. If I wasn't by myself, I probably would not have gone (or even have been invited). I agreed, and after showing me off to their roommates (they lived in a room of 10 girls), we went for dinner in their dorms.
The entire tour group. 3 guides and me.
When I returned to my hostel, it was still early so I went to the lounge. The great thing about hostels is that it's so easy to meet people. You have a guaranteed common interest--traveling. Grab a beer (or in my case on Christmas, there were free bottles of wine in my hostel) and start talking. Ask where they're from, where they visited, and where's next. Chances are, they have a good story or two. And the more you travel, it may be you who has the interesting story. This leads to the last question, "What if something goes wrong?"
The best stories are when something doesn't go according to plan. When you travel in a group, unplanned hiccups can be disastrous. More often than not, you already planned where you're staying and where you're going since it's harder to book things in a group. When it's just you, though, you decide where and when to go. If you want to do something, your vote is the only one that matters. I ate the heart, blood, and venom of a cobra; went on a three day motorcycle tour of Ho Chi Minh Trail; and decided to got scuba diving just because I could. I didn't plan it, but because I wasn't in a group, I was much more open to random opportunities.
What was supposed to be 1 day of travel became 3 full days through the mountains
When I travel, I have an checklist for things I want to do in places. However, the more you talk to people and find out their stories, the more that gets added to it. Even so, some of the best experiences will still deviate from your list. In a group, you lose that flexibility to do something on a whim.
Of course there are benefits to traveling with other people. For my time in Vietnam, though, I would not have done it any differently.