For example, consider how much "Number of Facebook users * average user income" will grow over the next 10 years. Over the past 40 years world GDP per capita has risen about 4.5% per year [1]. A portion of this growth was due to China's economic boom so outside of China we might expect GDP per capita to grow a little less over the next decade - let's say 3.5% per year ie. 41% in total. But world population is growing and Facebook's penetration is growing on top of that (albeit mostly into poorer countries) so it's reasonable to push that estimate from 41% to 50% or 60%.
Regarding "Effectiveness of an average Facebook ad" here's my experience: In April 2017, Apple released a new Macbook Pro. It looked great - fast, sleek, beautiful. So I visited the Apple website, clicked 'Buy Now' and chose my configuration options. But when I got to the credit card payment screen I had second thoughts - it's very expensive and my old computer was still working fine. Plus I wasn't really sure if I wanted the one with the Touch Bar or regular keys. So I decided to think about it a bit more. And for the next 6 months I was undecided - occasionally going back to Apple's website to drool over the specs - until I finally bought it a few weeks ago. Within those 6 months I didn't see a single Facebook ad for a Macbook. So there is still some low hanging fruit for Facebook to pluck.
For example, consider how much "Number of Facebook users * average user income" will grow over the next 10 years. Over the past 40 years world GDP per capita has risen about 4.5% per year [1]. A portion of this growth was due to China's economic boom so outside of China we might expect GDP per capita to grow a little less over the next decade - let's say 3.5% per year ie. 41% in total. But world population is growing and Facebook's penetration is growing on top of that (albeit mostly into poorer countries) so it's reasonable to push that estimate from 41% to 50% or 60%.
Regarding "Effectiveness of an average Facebook ad" here's my experience: In April 2017, Apple released a new Macbook Pro. It looked great - fast, sleek, beautiful. So I visited the Apple website, clicked 'Buy Now' and chose my configuration options. But when I got to the credit card payment screen I had second thoughts - it's very expensive and my old computer was still working fine. Plus I wasn't really sure if I wanted the one with the Touch Bar or regular keys. So I decided to think about it a bit more. And for the next 6 months I was undecided - occasionally going back to Apple's website to drool over the specs - until I finally bought it a few weeks ago. Within those 6 months I didn't see a single Facebook ad for a Macbook. So there is still some low hanging fruit for Facebook to pluck.
[1] https://data.worldbank.org/indicator/NY.GDP.PCAP.CD