" The fact that a statement is true may sometimes help to explain why it appears to us as self-evident. This is the case with ‘2 + 2 = 4’, or with the sentence ‘the sun radiates light as well as heat’. But the opposite is clearly not the case. The fact that a sentence appears to some or even to all of us to be ‘self-evident’, that is to say, the fact that some or even all of us believe firmly in its truth and cannot conceive of its falsity, is no reason why it should be true. (The fact that we are unable to conceive of the falsity of a statement is in many cases only a reason for suspecting that our power of imagination is deficient or undeveloped.) It is one of the gravest mistakes if a philosophy ever offers self-evidence as an argument in favour of the truth of a sentence; yet this is done by practically all idealist philosophies. It shows that idealist philosophies are often systems of apologetics for some dogmatic beliefs. "

― Karl Popper , The Open Society and Its Enemies