I like David Einhorn, though I don’t know him (at least as far as I know, he was a year or two ahead of me in school, at the same University and in the same major, so perhaps we shared a beer or a study session at some point), but someone has to remind him to stop shorting stocks just because they’re expensive and he thinks they’re in a bubble.

Einhorn, a well-known and widely-followed value investor who rose to prominence with a takedown of Allied Capital years ago and has been a big-ticket presenter on the investment conference circuit, put Tesla (TSLA) and Amazon (AMZN) into a “Bubble Basket” for his Greenlight Hedge Fund, shorting them and some other “richly valued” stocks because he believed they had little margin for error last year… and that may well end up being the proper analysis of these high flyers in the end, but when you have brokers making you cover your short positions or deposit more cash to cover the margin (because Amazon just about doubled last year, for example), and when you have investors watching your fund for performance each quarter after a long period of generally weak performance, you can’t afford to be stubborn. Einhorn’s fund reportedly lost 6.6% in value just in the month of January, a month where the S&P 500 rose almost 6& and the Nasdaq, home to many of those “bubble basket” stocks, rose 8% (and, of course, some of those particular stocks did even better — TSLA up 12%, AMZN up more than 20% going into earnings — in one month).

This is why most people don’t talk about their short positions — not only does it make everyone else kind of grouchy, with some mistaken notion that it’s “unAmerican” to bet against stocks, but it tends to get a lot of attention and there’s a lot of shadenfreude rolling around whenever you turn out to be wrong. Just ask Bill Ackman, who is often mentioned in the same breath as Einhorn and has been trying to dig out of the hole he blasted with his long-Valeant and short-Herbalife dynamite for a couple years now. (I’ve invested in vehicles run by both of those folks in the past, to be clear, without any gain… I’m not invested in them now).

Part of the challenge here, at a time when most of us ...