Everything you know about the world arrives through your own consciousness. You have never encountered a physical object directly — only experiences of one. You have never met another mind, only bodies that behave as though minds were behind them. Solipsism takes that observation seriously and refuses to step past it.
The position sharpens into two claims worth separating. Metaphysical solipsism holds that only your mind actually exists, everything else being its content. Epistemological solipsism makes the weaker and much stronger claim: other things may well exist, but you cannot know it — your evidence never escapes your own experience. The second is far harder to dismiss, and it is what philosophers usually engage with.
Its resilience comes from a structural trick. Any argument against solipsism must reach you somehow: through observation, testimony, reasoning, other people's insistence that they are conscious. But every one of those channels runs through your experience, which is precisely what is in doubt. Even a scientific demonstration is an experience of a demonstration. The position is sealed from the inside, and that sealing is its whole strength.
Yet almost no philosopher holds it, and the reasons are instructive. A theory that cannot be refuted also cannot be supported, and it buys its safety by explaining nothing at all. It cannot say why experience is so relentlessly surprising, why it contains things you never wanted and could not have invented, why it obeys stable laws you had to discover rather than decree. Wittgenstein pressed a further objection: the very language in which solipsism is stated is a public, shared instrument, so the position undercuts itself in the act of being expressed. And a common-sense point stands unrefuted — a view can be logically unassailable and still be no reason to believe anything.
What survives is the genuinely hard residue: the problem of other minds. You infer that others are conscious from behaviour and physical similarity, but you never verify it directly. That inference looks overwhelmingly reasonable and remains, strictly, an inference — which is why the question sits so close to debates about consciousness, artificial minds, and what it would even take to know that something else has an inside.