If someone arrived and gave us a lot of money to develop an idea we had, even without knowing much about it, we would try to pinch ourselves to make sure we are not dreaming. In the work world it is better to have a small failure today rather than a big failure tomorrow and this is where proof of concept comes in.
A POC verifies the technical feasibility of a project and the feedback of the potential users and consumers, giving indicators on the opportunity to continue and invest time and money in that direction. The POC is a light prototype of all the side functions which is concentrated on the validation of what is essential. Since it does not have what it takes to be a fully functioning product, before reaching the market, it is usually delivered to a limited number of testers.
Investors appreciate POCs because they allow them to test the water with small sums and understand how much the return on investment could be before funding a startup. Project managers use POCs to identify the issues in the processes that could keep the project from being successful on the market.