I am surprised how pessimistic most people were on the Switch. I thought it was pretty obvious that the Switch would do well from the get go.
I guess most people assume the previous generation affects the next generation. Clearly it doesn't. The Gamecube sold terribly. The Wii sold amazingly well. One did not affect the other. And also the Wii's success didn't help the Wii U at all. Likewise the PS2 was the best selling console of all time. The PS3 was a financial failure. Every generation is a huge reset button. Each console has to be evaluated on its own merits instead of basing it on the previous console.
I think group psychology might have had something to do with it. This thread was made right after the Switch presentation in January 2017, and a lot of people (especially on this site) were extremely negative about it. When people constantly see everyone else talk about how bad something was, they start to get a more and more negative feel from it themselves.
My prediction was 70 million, which may not seem much now, but back then I was constantly wondering if I wasn't overestimating it (considering how low most people's predictions were).