Investment in marketing and advertising

Hello! I assume that probably many people on the portal run their own business, so the question - what experience do you have with investing in advertising and marketing? Have you ever tried to calculate MROI for your investments in these areas? What is the most common level? Let's share our knowledge and good practices - please write briefly in which industry you operate and what investment in marketing or advertising brought you impressive MROI, and what turned out to be a total failure? Why do you suspect why it had such an effect?