Why is it universally assumed that corporate shareholders are incapable of looking at a big picture? If there were such a systematic error in the market, then

Why is it universally assumed that corporate shareholders are incapable of looking at a big picture? If there were such a systematic error in the market, then a smart investor could really make a killing by investing in the artificially-cheap stock of long-planning corporations. And, of course, such an investor would have a very impressive history after a while, and be able to command quite a bit of money managing investments for others... which of course leads to greater sums of money being invested more intelligently. The market fixes itself.