Ray Dalio gives the best explanation to why the business cycle exists [1]. I wish I could provide a TLDR that does the video justice, but there's just too much great insight in this video to condense it any further (it's only 30 minutes anyways). In my opinion, this should be required viewing for all financially literate adults.

[1] https://www.youtube.com/watch?v=PHe0bXAIuk0