Let's say you own a pile of X. If the value of X only fluctuates a few percent per year, like a major currency, you will freely trade your X for stuff, because

Let's say you own a pile of X. If the value of X only fluctuates a few percent per year, like a major currency, you will freely trade your X for stuff, because you can always get more or less the same amount of stuff in the future. But if the value of X is changing 10% or more per year (or per day), you will either exchange as little X as possible if it's going up, or dump it all if it's going down.