The invisible hand of the market will let you know what aspect of your output is most valuable for others.
The benefit of this invisible hand is that the "economy" as a whole does not need to know how good they are at producing everything. People just need to know if what they are producing now is more valuable than the next best alternative. Everything else will be sorted out with market forces.
In university lectures we were given the famous argument about olive oil from Greece and that it would never make sense to do our own olive oil because we both lack the natural resources (unique soil + sunshine) which allow olive trees to grow easily and we'd also have much better yields growing other things on the fields.
So to me, both opportunity cost and comparative advantage are really basic building blocks of economic understanding and I'm a bit dumbfounded that someone wouldn't understand these concepts.