Last year, I got an email from a college friend who reminded me that I'd told him to buy MSFT shares in 1986. Neither he nor I did, so I file this in my 'Woulda, Coulda, Shoulda' file, alongside similar stories about Cisco in 1991, Netflix in 2001, and Bitcoin in 2011.
I remember looking into Bitcoin in 2012, and thinking:
"This will never work as a currency, because of the max number of bitcoins it will inherently be deflationary, and the value will go up, which means that there will be a disincentive to spend it, because the value will just go up..."
Yep... Did not buy any.