Fresh fiat is one way for the market to go up.  But it's not the only way.  Every time someone sells, they may buy back at a higher price.  The guy he sold to may also be buying back at a higher price.  The "don't want to miss the train" can cause a great deal of this.  To get ever higher highs without new fiat, the market must sell more rationally than it buys.  The process of unwinding positions must move the price less than the process of opening long positions.