A PE beyond 10 is ALWAYS BAD for an investor, because it means you are MOST LIKELY TO LOSE MONEY because you BOUGHT at a HIGH PRICE. Also, it is FALSE that historical PE are 15 to 20. False. Historicals bounce around 10; only for good companies. If you take a long enough period. PROBLEM is that the recent decade to 2 decade have been skewed as the ignorant and novice masses have come into the stock market since Internet and Brokerage accounts got merged. On top of that, misleading posts of jerks on the Internet and media pushing that the concept that a PE of 15 is normal. IT IS NOT. If you take away the last decade of bad PE ratios, then you will no longer see a 15 to 20 PE, and you will see 7 to 10 PE AS THE NORM for ONLY A GOOD GROWING COMPANY. ONLY for those. Exceptions exist for very high flying, cutting edge tech companies, super growth companies, in which case a PE of 15 is acceptable, but those are very rare. Again RARE, & should be so. $IBM $SPY $COMPQ $DJIA