The best investments are often made with people that have a plan. It's for this reason that just about every checklist for starting a business has "Write Business Plan" somewhere near the top.
A core concept could be considered the business plan of a game. If the developer asking for money doesn't have any concept art, a prototype build of the game, or any real idea what the final game is supposed to be, that shows a lack of a plan. So goes the saying, "Failing to Plan is Planning to Fail."