The book A Random Walk Down Wall Street proposed the Random Walk theory.
It says that share / security prices change randomly – and hence cannot be predicted by charts or technical analysis. Price changes are like a person out for a walk – they can change direction at a whim.
Chart and technical analysts will argue fiercely that they can predict future price movements.
We think that both are right! Prices do move randomly, but technical analysis does provide a good guess about the path ahead.