Market Timing

The fundamental approach to investment requires one to work out the intrinsic value of a share before its purchase. 

"Why don't we just wait until the whole market is low enough and then go in and buy a wide selection of shares?" 

This question suggests that one invests by means of "market timing". If practical, it will surely save us a lot of time and effort. 

• Is it possible to carry out consistently correct market timing? 
• How easy or difficult is the art of of market timing?