It means that the distinction between what seems to be reality and what reality really is,
the thing in itself, is finally given up. To Plato, the realm of ideas was was more real than the world of appearances he lived in. This myth of a truth behind the world, written in mathematical or religious terms, has pervaded western thought ever since. Pragmatists aim to be a little more realistic. Man is not the great representer of that true reality, but just a 'clever animal' that figures out 'better and better ways' to get by.
This might enlighten you further.