Hostels can be really great for meeting people, especially when you’re travelling alone. Mostly you’d come across other travellers in the common area, or the kitchen, but it may even be that you end up connecting with people you share a dorm with.
However this falls down a bit where you have a night or two where the hostel is dominated by a small insular group, often with whom you don’t share a common-enough language. This is especially a problem in small hostels. The small group will dominate the communal areas, talking only with each other, and everyone else ends up feeling a little isolated.
Sometimes you can be travelling alone, even surrounded by other people.