which your 401k is valued in, has lost considerable value. The dollar amount of your 401k has increased but the value of the dollar itself has actually decreased.
That is the illusion. The FED prints money which causes Wall Street to have a temporary "rally" and go back up so that the amount that the dollar, what the 401k is valued in, has decreased from this money printing becomes overlooked because people have a false sense of newfound security to see a higher number on their 401k statement. But in essence, the 401k has essentially stayed the same in terms of purchasing power, which is the only thing that really matters. It has only increased by the amount the purchasing power of the dollar has decreased.