[bolu]

Your point about the single month as the timing period is definitely valid - in hindsight the article would have benefitted from having that be maybe 6 months or 12 months instead.

The premise isn't as clear-cut as what you laid out, in my opinion. In general people do start with the best of intentions; that is, their time horizon when they buy is usually something like "until I need the money". But, that's the generic case under stable market return conditions. In times of panic, folks who thought they were okay with risk find out they're not okay with it, and pull out (usually after much of the panic has already passed). In boom times people start to, like you said, "move money between funds" usually in a way that follows the recent price increases (gold recently, tech in 2001, etc). It's these movements that the article is written against - and you're right, it would have benefitted from a longer time series of returns.

Indeed, if you remember the oft-quoted Nasdaq Composite Index from the dot com boom - the level in 1998 was the same level as in 2002, but in the interim investors as a whole lost billions. That's a lot more than would have been lost if people had just regularly been investing the same amount each month into their 401(k), which is what we wish would have happened.