Long-term it is hard to justify a conclusion that cryptocurrencies will fail as a technology. It's too big of a leap forward in too many industries. Short term, bitcoin might move too slowly and be surpassed by a competitor, or big money might manipulate the market and take advantage of people who have no idea what they're doing. I see these as issues that will diminish and fade over time as the technology matures. The solution is to stay attentive, invest with caution and hold on through the booms and busts. Not hard to do, all said and done, though I understand why many fear it.