Here is an interesting post:
http://aswathdamodaran.blogspot.com/2019/09/insights-on-vc-p…
Basically, the author Professor Damodaran, by observing the hot unicorn IPOs this year, concluded that the VC culture has encouraged many unicorns to make completely insane claims on their respective TAM ($5.7 trillion for UBER, $3 trillion for WeWork, etc), as well as how fast they are scaling up into the TAM.
The examples in the article are completely different from stocks discussed on this board, for sure. But I think when we project TAM for the SaaS stocks, it is prudent to try to be as realistic as possible.