A common heuristic for estimating the quality of something is: what has it done for me lately? For example, you could estimate the quality of a restaurant via a sum or average of how much you’ve enjoyed your meals there. Or you might weight recent visits more, since quality may change over time. Such methods are simple and robust, but they aren’t usually the best. For example, if you know of others who ate at that restaurant, their meal enjoyment is also data, data that can improve your quality estimate. Yes, those other people might have different meal priorities, and that may be a reason to give their meals less weight than your meals. But still, their data is useful.