Most investors learn this the hard way: a diversified portfolio of mediocre bets doesn't save you. One fund-returner does. That's the power law, and it shapes every single decision a serious early-stage investor makes.
In a typical 20-company angel portfolio, roughly 15 companies will return nothing or pennies. Three will return 1x to 3x. One or two will drive 80% or more of your total returns. This isn't pessimism. It's the observed distribution across decades of venture data from Cambridge Associates, Kauffman Foundation, and individual fund track records alike.
What this means practically: your job isn't to avoid bad investments. You can't. Your job is to make sure you're actually in the deals with a realistic path to 20x or 50x, and that you're not so conservative on entry that you price yourself out of the upside.
The math you need to hold in your head
Write ten $10,000 checks ($100k deployed). Nine go to zero. You need the tenth to return at least $100k just to break even. To make angel investing worthwhile as an asset class, that tenth probably needs to return $300k to $500k minimum, which means you need companies that can genuinely reach $50M to $200M or more in exit value.
That filter alone kills most pitches before you open a deck. If a founder can't articulate a credible path to a $100M-plus outcome, the math doesn't work for you as an investor, regardless of how good the team is. Hold this framework throughout the course. Every evaluation question connects back here.