Traders are willing to pay for any asset what they deem fair (aka the art of trading). The underlying principle dictates that, if there is an unbalance in supply or demand equation; then, with certainty, that price will change (the science of trading).
Trends are easy to spot after they have already happened. The art and science of trend following is to detect a trend in ‘real time’ with probability scenario of the trade, is mandatory for professional traders. Because they don’t chase the market. How exactly this is executed is what makes the best investors in the world from the rest.