Explain: If the price of silver has shot up so suddenly, would it not be difficult to sell?

So, I have a friend who bought a bunch of silver a few years ago. He was telling our friends how valuable it will be in the future. We all laughed it off. But, now the price of silver has gone up quite substantially. It has really got me thinking. If something such as a precious metal shoots up so suddenly, is that potentially a bad sign that it could just be unstable, making it a risk for potential buyers. For example, if someone invested in silver a few years ago, and decides to sell it now, would it not be difficult to find a buyer due to risk of it just dropping in value suddenly again. In the eyes of a buyer, would a gradual increase in value, opposed to a sudden one be a better sign, and more of a safe investment at this point? And, I understand it is an important metal for some industries, but if the price goes too high why wouldn't they just find an alternative metal?

Sorry maybe, and very confused series of questions, but I am genuinely interested.