how can we believe anything??

[Thumpalumpacus]

You can only know what you know through your senses, and that's about it.

In one sense -- pun intended -- that's true. But in another view, you can compare your sensory inputs with those of others, and use corroboration or disagreement to come to a finer understanding of reality.

Now, if you want to say that your brain is practicing an inherent solipsism, that's a fair objection, I suppose -- so long as you can explain the evolutionary value of such a cognitive view.