What can result from cooking sugar at too high of a temperature?

Cooking sugar at too high of a temperature leads to caramelization, where the sugar molecules begin to break down and develop complex flavors and colors. However, if the sugar is overheated beyond the point of caramelization, it can burn, resulting in a bitter taste and dark coloration. This burnt sugar loses its desirable qualities and can negatively affect the overall flavor and appearance of a dish.

The other outcomes mentioned do not accurately describe the effects of overheating sugar. A clear and robust syrup is achieved by cooking sugar to a controlled temperature, while perfectly cooked sugar means it has reached the right stage without burning. A thin and watery syrup suggests that there hasn't been enough cooking or concentration of the sugar, which is contrary to the results of cooking at excessive temperatures. Thus, the significant consequence of heating sugar too much is indeed the production of burnt sugar.