This depends very heavily on the product. With some products, for example food, you have to win your customer back every month. Additionally, it is often very d

This depends very heavily on the product. With some products, for example food, you have to win your customer back every month. Additionally, it is often very difficult to correlate certain kinds of ads to sales...but if you look at the marketing investment over decades in some industries, it is probably the only source of competitive advantage. That being said, given that most people here work for tech companies, I do suspect there is huge overinvestment into marketing by tech companies. Some companies just don't do any of this, don't have a sales team, don't have a marketing team...and they do fine. But that isn't universal (for example, sales clearly has an important implementation role in some industries, in some industries sales has an organizational role, etc.).