What makes the stamp precious is rarity, demand and good condition. There are many philatic gems which are much sought after. Many of these are stamps with errors in printing(this rarely occurs, this makes it expensive, depending on their demand). A good example is the one penny Mauritius stamp of 1847 on which the inscription happened to be “post office” instead of “post paid”, by mistake. There are hundreds of stamps which are valued above 1,000$(but I don’t have any even though they are in hundreds!!!).