The Efficient Market Hypothesis is obviously, patently false. The markets cannot agree on the value of an asset from week to week, day, hour, minute or second. Equities in stable businesses with millions of shares traded daily see their prices fluctuate 5%, 10%, 20% intra-day. The tangible value of a company simply does not change that fast. It doesn't.

It's impossible to time the market perfectly every time because that would imply perfect knowledge of the moves of all the participants. By the same token, it's impossible to mis-time the market every time, because then you could just take all the opposite moves and you're back to winning. It is possible to win more than you lose, not by being the smartest, but simply by being smarter than the average participant. Which, thanks to companies like Robinhood putting trading capability into the hands of any naive smartphone owner, has become easier than ever.