What is most important to know before buying a stock

If you were offered a kilo of saffron, an orange powder used as a spice, for R$ 10 thousand, would you buy it? If you said no, we understand your gut. The price really seems absurd for a seasoning. However, a kilo of true saffron (different from turmeric, called saffron of the earth) today revolves around R$ 100 thousand, so you could resell this purchase for 10x more, even if you never intended to use something like that in food. There is only one difference between people who would be able to take advantage of the opportunity and those who would pass up the offer: the first group knows how much saffron is worth. Similarly, it is only possible to invest in shares in a promising way knowing the value of what you are buying. Without this notion of value, how would you know when the stock is cheap enough to decide to buy it or expensive enough to decide to sell it?