Firstly, there is risk associated with a perceived level of certainty. Using your example, there is risk that a marketplace for a something will not be accessible and operational, although a perceived level of 100% certainty against such a scenario may exist. Additionally there is risk in that the something will not or can not be sold for zero or better, again irrespective of a perceived level of certainty. As it relates to trading, IMO, certainty is perceived, usually garnered through scientific and/or experiential means. Risk is ever present regardless of the perceived level of certainty.
So zooming out to the highest level, risk is epistemological uncertainty - the limits of our ability to understand reality. Using this definition for trading would mean that risk is not so much about fluctuations around the expected value but about the accuracy of the expected value itself. Since our expected values never represent reality, risk becomes proportional to the robustness of our probabilistic judgement - where robustness is defined as the balance between the weight that we give to inferring the future from the past (frequency) and the weight that we give to the most recent past (the present dynamic).
As it relates to trading, I agree, with exception to "expected values never represent reality". On a side note I think you and I both need to get out more. PS. good word... epistemological
Trying to avoid the philosophical .... When it comes to trading I think it is only hindsight that will give you a true level of certainty....the rest is perceived of course, and why I think its generally a best guess. But keeping with the trading example of buying something for zero.....it was the only real risk free trade I can think of off the top of the head.. What is the risk here ? (you have already bought it so we are not talking about the risk of not being able to buy it, and if you cannot buy it then its not a trade and hence no risk - and even if there is a risk you might not be able to sell it again, there might not be any loss of value....no off course sitting in cash is a risk, but in this case to buy something at zero you dont need cash. ) Edit: revise this after 30 secs of thinking - it clearly depends on what you are buying. Sometimes you can get an asset at zero that liabilities attached to it, or storage costs etc....been in the financial never never world of non-real items for to long!