Valuations are based on expectations of future profit. If people's perceptions about Apple's profitability drastically change from one moment to the next (such as the day before the watch is released for sale and the day sales figures get reported), AAPL can easily increase 50% over the next 13.5 months. (Or go the opposite way.) Look, Nov 22 last year, AAPL was at 74.26, today it's around 115. That's about a 45% increase in a year.