Self-learning is improved when you learn alongside others.
But isn't this paradoxical? If others are present, isn't that the antithesis of self-learning?
By sharing questions and answers with each other, we learn from each other, see how others think, and how they learn. This sharpens our sense of self, and improves individual learning processes. It's also more fun.
Of course, all learning is in some sense self- and in some sense collaborative. It is individuals who learn, but learning comes by way of other people. Either in person, or through books, etc.