It is a striking and intriguing aspect of modern intellectual life that metaphysics is invisible to almost everyone - despite that it was the very first type of philosophy and formed the basis of the subject (off and on) from the Ancient Greeks onwards.
Metaphysics refers to the fundamental assumptions - and therefore it is by definition not susceptible to proof or disproof nor does it depend on evidence. Even this by-definition fact is beyond modern Man.
This may be evidence of a decline in both average and peak intelligence, since it was only ever the most abstract thinkers who could engage with metaphysics.
Or, it may be due to a loss of introspective ability - although superficially modern people are far more introspective than people of the past; alternatively it may not be the loss of introspective ability so much as the belief that introspection is insignificant, merely 'subjective'.
The mainstream metaphysical beliefs of modern Man (because of course he has them, even if he does not know that he has, and denies the fact) are therefore utterly invisible.
(The most obvious example of invisible metaphysics is the theory of evolution by natural selection; another would be the assumption in physics of fundamental randomness - and therefore non-causality; another (related to the preceding) would be that a human life has no objective purpose or meaning.)
Modern man can only observe the consequences of his own metaphysics; but without even the slightest comprehension that these are necessary and predictable consequences of his own assumptions!