The greater fool theory does not apply to such a uniquely valued company.
In history there has been many situation where mania and artificially inflated prices have prevailed for a time and then an implosion followed.
I know one that I took part in around 2000 with the crazy values of hundreds of internet companies that earned no money yet their share prices were selling and in demand. I remember making profits of $25K on trading csco systems. It went on for several weeks... then the bubble burst. I lost most of my 250K value portfolio.
I've read about the "Tulip Mania" several centuries ago. One tulip was sold then for hundreds of dollars... Amazing, yet there was no value there.
However, Tesla, Inc. itself is of great value company. Growth companies command very high PE ratios. I remember Amazon using all its revenues to expand and grow the company for a decade or more without giving any dividends. I bought the stock few shares but missed the boat as I sold it before the share price rise came. I knew it was a good company but I was impatient. But I learned a lesson then. I will be more patient with my TSLA because of it.
As to the larger market PE I think anytime when above 20 is getting into a high territory. Probably we may experience a recession like in the aftermath of the 207 financial debacle but even the Coronavirus has not shaken the US economy.
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