DISCLAIMER: Views not necessarily my own
I think it would be hard to try to pinpoint a single point in time where "he lost it". Stephen Wolfram grew up as a mathematician/physicist wunderkind, so as it's often the case for people that produced highly praised work early in their life, it's hard to transition to a life with humbleness and where output is received with anything else than praise.
In the past he has made a number of outlandish claims that didn't bear fruit (predictably so), to an extent that one would think that only a delusional person could make them.
E.g. he did a lot of work on cellular automata, and wrote a book titled "A new kind of science", in which he predicted that cellular automata would revolutionize all kinds of natural sciences (hint: that didn't happen). He later made similar claims for Wolfram Alpha revolutionizing search engines, and the Wolfram language revolutionizing programming.
This multi computational idea seems to draw from the double slit experiment where observation collapses the wave function and the multi-probability path history based on the observer. This is saying that computations can be modeled similarly. And this type of model handles non-determinism in general and "threads of time" apparently. Interesting. Ambitious but very interesting.
However I think a lot of that narcissism is confidence justified by his successes and track record, he’s created a lot of value for the world.
Funny, I see it as the entire opposite: very extreme insecurity, the need to constantly remind us that, yes, truly, he was there, he pioneered this, it _is_ amazing and awesome and will revolutionize everything, believe me, and it's only second to this other thing, which we must remind you, I invented.
A confident person would strip away the fluff and just get on with the message?
Narcissism more often comes from hidden or repressed insecurity - the opposite of confidence.
We all have insecurities- I’m sure even Mr Wolfram.
But success also leads to confidence. An entrepreneur has to pitch his brand and “wolfram” is his strongest brand.
Would love if someone massively successful explains what that feels like