But it's not an unreasonable approach. Declines are often driven by panic. If you can determine that it's an irrational panic and the fundamentals of the business remain strong, then you can invest while it's undervalued. It's certainly better than buying just after something has gone _up_.
Well, yes, that might have informed his lessons from trading. There's another saying in the opposite direction, "never try to catch a falling knife". https://www.ecb.europa.eu/pub/pdf/scpwps/ecbwp1545.pdf
But it's not an unreasonable approach. Declines are often driven by panic. If you can determine that it's an irrational panic and the fundamentals of the business remain strong, then you can invest while it's undervalued. It's certainly better than buying just after something has gone _up_.