I had a cautionary example from some sales guys I worked with, who got caught up in margin calls – one burned the wedding money his wife had ear-marked for a house. I had avoided stocks like Cisco with wild P/E ratios and my portfolio made good returns throughout this period because it was diversified, but if I’d been willing to bet higher on Apple I would’ve retired early so I appreciate the allure.
You don't know anyone retired, unemployed, or employed but spending all that they currently earn due to having kids etc?
You clearly don't follow very many "meme stock" communities.
https://www.investopedia.com/ask/answers/09/difference-betwe...
Since investing 100% in a single stock makes one a speculator, not investor, then by definition no investor invests 100% in a single stock.