I do not think it is a good basis for people to sell their Bitcoin if the price is HIGH because such is highly subjective- what is high for you may not be high for me. Also, while it is good to presume that investors have a fair understanding on what is a high price from a low price, I do not think knowing such per se is already a good indicator to sell. Sometimes, rather, more often than not, it is best to know how much money you have invested and take into consideration the inflation rate with reference to return of investment AND return on investment. With this, you have to keep abreast how the USD is doing for you to have a benchmark on how much you have earned or lost in the process. The latter statement serves only as a guide but is NOT determinative of the value of your Bitcoin wealth since we all should know how rapidly fluctuating the value of Bitcoin is.