We come across recommendation systems on almost a daily basis, whether you are buying stuff from Amazon, watching movies on Netflix, playing games on Xbox, finding news articles on Google, or listening to music with Spotify. These online applications recommend items based on your previous history, or users who have similar interests.
Figure 9.1: Recommendation system on Amazon
Why has recommendation become such a big thing in our lives when 15-20 years ago in a typical brick and mortar store this was unheard of? The answer lies in the fact that we are now in an era of abundance rather than scarcity. Let's drill down a bit more into this. 20 years ago, the number of products that a typical retailer stocked were limited. The reason is the limit of shelf space and expensive real estate cost.
Similarly, our favourite movie shop would only contain a limited number of movies and our book seller would contain a limited number of books. I still remember 20 years ago...