It's form, the bell shaped curve, is a graphic of market behavior. Prices above and below the two SD's are outside the day's distribution. So the day's high and low may actually not be a part of the day distribution. Anyone can see from the Market Profile that the high and low were rejected quickly by the market. Using these prices for trading decisions as the Candlesticks method does, is simply making important decisions from poor data .
Most technical calculations use the same data and suffer the same defect.
The day's high and low prices are called excess because the high and low are too far from value, the main body of the day's trading. Efficient markets, where information is immediately piped into the market would not have the low volume highs and lows. There would be no excess. Instead of the bell shape, the day's distribution would be an elongated block. Market Profiles show over and over that markets are not efficient.