Do not listen to analysts , they are always the last to go bearish . example AAPL , only now are the doing so.
Rule 2 .
Never use PE as a valution ratio at ,market tops . If you must use a ratio like that use P/S .
Rule 3 .
The ONLY real measur of how much you are paying for stocks is the same one Warren Buffet used .
That is stock price to Book value known as P/B .
Judging many stocks by that measure today they are the highest in history by a very long shot.
Two examples stand out .
UPS one of the leading stocks in the Dow Transportation index is 17.5 time book value OR 44.45 IF you use the Tangible book value.
IBM as lead stock in the DOW has a .Price to book of 12.5 (4 times AAPL) or infinity if you use its Tangible Book value of Minus $12.72 per share .
With lead stocks like that in these indexes no wonder the NYSE has one day circuit breakers of 10-30% .