IE: Deflationary Spiral. It becomes hard to be a merchant who accepts bitcoins, because everyone expects BTC to keep rising in prices.
People who bought a domain name for 1 BTC a few weeks ago from Namecheap lost a lot of money. They should have instead "saved" that BTC. Therefore, people are discouraged from using BTC as a transaction vehicle.
Currently, hoarders are the ones benefiting from BTC, but no one else is. No merchant knows how to value their services in BTC, not when there is this much volatility around.