Not all ex-post theories are BS. For example, I slam my hand in the drawer and theorize, "Slamming hands in drawers hurts; one should not do it." That theory is pretty solid. It doesn't cover all the edge cases, but following it is better than not following it. There are lots of startup theories that are equally solid, despite being ex-post. I know a startup that didn't pay payroll tax for a couple years, and it ende…
There's strong prior reason to believe not paying payroll tax is not going to end well. The theoretical basis is simple, clear, well-reasoned, and supported by strong evidence in adjacent realms (i.e. the IRS takes taxes taxes pretty seriously).
Whereas the prior on the validity of something like "early-stage founders should live with their customers" is much weaker.
Even though the advice for each presented example is based on sample size n=1, the resulting belief can and should be quite different depending on your prior.
The real meta-advice is to be able to understand and evaluate your prior for any given piece of advice you receive. This mostly comes down to thinking rationally, being knowledgeable, and critically considering each piece of advice for whether it's worth heeding or not.
Which is not so far from the author's message I think ("figure everything out yourself", "I don't mean to say don't take any advice").
(Obligatory shout-out to Bayes Theorem)