I like Patrick's restatement of the Practically Efficient Market Hypothesis:
You are astoundingly unlikely to know more about any stock from reading the newspaper, seeing their chart on Google Finance, or consuming their quarterly reports than a team of PhDs who did nothing but study that stock for the last year, and accordingly are vanishingly unlikely to trade stocks in such a fashion that you do better than the market once you account for fees and tax impact.
It gets to why these comment threads can sometimes have people talking past each other. Someone will say "You can't time the market", and mean 'you' in the same way Patrick does, but someone else will come along and think the statement meant "no one can time the market". Then the discussion goes off into a whole rabbit hole about quant hedge funds and the like.
Relating this back to techie-problems, perhaps we need the moderate Practically Secure Crypto Hypothesis:
"You are astoundingly unlikely to create something better and more-secure from seeing a blog-post, reading some Wikipedia articles, etc. than a team of PhDs who did nothing but study mathematical theory, cryptography, and code-breaking for the last few years, and accordingly are vanishingly unlikely to create a new scheme which is more secure than existing standards once you account for performance and maintenance."
Except that security standards are mostly driven by compatibility with all sorts of edge cases (ancient versions of software! COBOL-bound CAs! tiny smart cards! huge distributed systems!) that are probably not relevant to your case and create big random security holes.
If you have a reasonable way of distributing software updates, signed-DH with an AES-based AEAD with termination detection for transport authentication, and a signed hash tree for data authentication, is going to be more secure than RANDOM_SECURITY_STANDARD.
I don't think that's always a case of people talking past each other. I will often reply to someone (in much the same way you just did) with a clarification about how some people do predict the market successfully, because even if I charitably assume they understand this implicitly, I want to make sure the literal idea that no one is capable doing it is not spread around like a gospel for other readers.
You are astoundingly unlikely to know more about any stock from reading the newspaper, seeing their chart on Google Finance, or consuming their quarterly reports than a team of PhDs who did nothing but study that stock for the last year, and accordingly are vanishingly unlikely to trade stocks in such a fashion that you do better than the market once you account for fees and tax impact.
It gets to why these comment threads can sometimes have people talking past each other. Someone will say "You can't time the market", and mean 'you' in the same way Patrick does, but someone else will come along and think the statement meant "no one can time the market". Then the discussion goes off into a whole rabbit hole about quant hedge funds and the like.