No one will ever be sure of the market price of the items they are trying to sell as it fluctuates. If you choose to sell your shards at 20, that's because you don't think that it will sell if you put it at 40 (or that it will not sell fast enough, thus tying down your capital). I on the other hand believes that I can sell it at 40, so I'll buy yours, paying you up front, and took over the risk that you refuse to take. If I manage to sell it at 40, then the risk that I've taken paid off, and I'm rewarded. Else, I stand to lose some of the investments that I've made, or have my capital tied up in stock which I can't use it to invest in other goods. Just like in the real world, you get rewarded for taking risk. Succesful trader are just better at managing that risk than others through intepretation of various market signals and information.


I won't go as far as saying that you can't control the market...but you won't be able to control the market indefinately. The length of time you are able to hold on to the control is a function of your capital...and if that's finite, then your control duration is finite as well.