Do they actually say that? You should only invest in companies you understand, and being a user if the product helps with that, but that's a metric for weeding

Do they actually say that? You should only invest in companies you understand, and being a user if the product helps with that, but that's a metric for weeding out companies, not building a portfolio (i.e. if you dont understand them dont invest, but if you do it doesnt mean you should). The only real metric for investing is if you believe the expected value of the asset to you is greater than the market price. For example, I used moviepass, but I would never have invested in them because they were selling a dollar for 25 cents (which is why I used them...).