It is not a matter of Believing ... but a matter of Knowing.
For each single one of us is Aware ... In Life, of Being !
Thus, we "see" a thing, or things, as a matter of our our Visual Awareness ... just as we may Feel an abstract Sentiment, as a matter of what be essentially a Personal Experience ...
And though there could be the human Community of Sight and Sentiment ... yet its very rare, rather never, that all individuals ... See and Feel exact similarly.