Complex sentence: It is easy to spot a bottom after an upturn is well underway but it can be difficult to identify a bottom (referred to by investors as "bottom picking") while the market or stock is still in the decline.
Split into simpler sentences: It is easy to spot a bottom after an upturn is well underway. However it can be hard to predict a bottom (referred to by investors as "bottom picking") when a market is still in the decline.