Wikipedia:Truth, not verifiability
|This page in a nutshell: Wikipedia is supposed to reflect what reliable sources say, regardless of whether individual editors think it is true or think they can personally verify it.|
The de facto primary criterion for the inclusion of information in Wikipedia is truth, not verifiability – whether reliable sources state it to be true, not whether individual editors think they can verify it themselves.
You may have noticed that the de jure primary criterion, as stated on Wikipedia:Verifiability, basically puts this the other way round as verifiability, not truth: "Even if you're sure something is true, it must be verifiable before you can add it".
It does not really matter. The distinction being made here is not really between truth and verifiability at all, but between the statements made by reliable sources (which we want to include in the encyclopedia), and the unsupported claims of Wikipedia editors (which we don't).
It's not quite as simple as that, of course, but once you know that Wikipedia is supposed to reflect what reliable sources say, not its editors' private thoughts and unsourceable personal knowledge, most of the rest is more or less common sense.