The following section contains valid arguments for travelling alone or with others.
Travelling alone gives you much more exposure to the culture and people. Once people have travelled alone, they are rarely interested in having a companion for any length of time. It gives you more flexibility and freedom in your plans since you can go wherever you want, whenever you want. Meeting partners along the way is very easy, and I noticed that the women travelling alone quickly adjust, plus they tend to meet people to travel with when they need them.
Also, I met many companions that split-up after ugly arguments and misunderstandings on the road. I find that in most cases, "It's best to leave friends at home if you want to remain friends!"
"You are forced to meet more people for any sort of social interaction. Many people who travel in groups, even a group of two, find much of their time is spent dealing with the group and not the people of the country you are in. My wife and I decided to travel separately, she travelled, and when she came home I left. This made sure bills were paid, lawn was watered, investments looked after, etc." <Davy Davis>
"If you do travel alone successfully, you will return with such an enormous feeling of accomplishment and self-confidence that I sometimes recommend a solo trip to friends as therapy. The downside is occasional loneliness and the lack of someone to help you out of jams, but once you move beyond this and find your own inner strengths and abilities you will be exhilarated." <Larry Lustig>
"I have done a LOT of travelling throughout Africa & Asia and met a lot of other travellers on the way, and would say the most important bit of advice to give someone setting off, THE golden rule, is GO ALONE! Travelling is a very individual thing -- a companion forces you to make compromises. The dynamics between yourself and your companion intrude on the travelling and diminish the experience. A companion isolates you from others -- you become a social unit that excludes others joining in. Plus you will inevitably part company sooner or later anyway -- save yourself the grief and the wasted opportunities. There are many others on the road with whom you will team up for short periods anyway. There are plenty of watering holes en-route where you can meet up with other travellers when you find yourself needing social intercourse. There will always be others with whom you can share expenses (i.e. renting a car or guide) for short (< 1 month) excursions. Go on your own -- it's MUCH more fun. The only exception I would make to the above is if you have a wife/husband/partner without whom you would not want to be anywhere: and even then the travelling itself is still diminished - but the relationship is more important." <Nigel Gomm>
"One of the great truths gained while travelling comes when you immerse yourself in the ever-changing ebb-and-flow of chaotic events around you, the stream of teaming and amazing life going by. The constant presence and focus on a companion anchors you too much, and you miss the mystery. If you find a companion who shares this focus on the road, if the interaction is near zero maintenance, if you can "be alone together", then you may have the best of both worlds: the magic of the road, and the convenience of travelling as two. <R.S. LaMorte>
You will meet plenty of people in the hostels, guesthouses, and hotels. It is easy to get to know people in this situation. At times, you will probably travel with one or more people you meet along the way for days or months. The key is to realize everyone has widely differing interests and budgets, even though you enjoy each other's company. Know when and how to gracefully separate, even if just for the day, so you may remain friends after the trip.
"After talking to many travellers along the way, the common conclusion has been that, no matter who you leave home with, it is a good idea to plan for doing some parts of the trip separately, if each person is comfortable with that. Just because you are interested in doing different things at certain stages of the trip should not mean you have to part on bad terms and never meet up again. Besides, a few days apart does wonders if you're getting sick of each other!" <Dave Patton>
"I found the best time to meet others was during the transportation phase between cities. Travelers usually band together for the 'duration' and commonly need the same types of shelter at the destination point. Once others have moved into town and setup their accommodations, it is harder to join their party than if you were all in it since the moment you stepped off the bus/train/boat." <Alan Nelson>
A final note: trying to rendezvous with other travelers (and your Poste Restante mail) in distant cities gives you deadlines that limit your ability to stay in places that you like since you are trying to keep to a schedule, and it tends not to work half of the time.
Travelling with others provides added security, lower accommodation costs when sharing rooms, and less weight when packing shared equipment.
"Having a companion to stay with the luggage (restaurants are good places to leave them) while you try to find that great, cheap guesthouse can be a real boon. You are not in a good position to bargain for rates if you have been slogging 10 kilometers in the rain with a heavy pack." <Larry Cotter>
Choose your partner(s) well, because you will probably spend every moment together from start to finish. This may seem obvious, but there will be times when feelings get hurt in the decision-making process. More importantly, do you trust them when the going gets rough? You may have to rely on them if your health deteriorates, or an 'unsafe' situation arises. There are plenty of travel partners who have been abandoned in the middle of the trip. Always be sure that you could cope on your own if need be -- it may happen through argument, sickness or any number of other factors. Be prepared.
Note: If your companion has a different passport-nationality, both of you may not be able to get the same visas.
Make sure you have compatible personalities, objectives, interests, budgets, spending patterns, and similar levels of fitness long before you leave. They should be able to carry their own load, unless you want to carry it. Read the section on "Goal or Purpose" at the beginning of the guide.
If you are a couple, you might want to read "Traveling While Married: How to Take a Trip with Your Spouse, and Come Back Together" by Mary-Lou Weisman.
You will need to spend some time together, like a whole weekend living out of your backpacks and travelling around your city for 8+ hours a day using public transportation, or go on a camping trip. Discuss objectives and how problems will be solved. "Discuss in advance what happens if you want to split. Would it be possible? A couple may end up with a male travelling alone (no trouble), and a woman having to go home since she does not feel comfortable travelling alone." <Mats Henricson>
"Make sure you understand how to do a 'time out'. There *will* be times when your interests will not be satisfied doing things with your companion. Plan for a day or two when you travel separately in the same city, doing things which you would not do with the other person. It works wonders." <Henry Mensch>
"This is harder to do than it sounds for the very reason it is so necessary: you become dependent on each other, unable to experience the culture alone. Do it even if you do not feel the need, you will not be sorry." <Larry Lustig>
"Another big compatibility issue is how to handle hooking up with yet another person, especially if there is a potential romance in the offing." <Miriam Nadel>
If you do not have a travel partner, there are organizations that will help you find travel mates.
Connecting: Solo Travel Network
Lonely Planet's Thorn Tree: Find Companions