Timing the market is practically and emotionally impossible

 As the Danish philosopher Soren Kierkegaard noted, life can only be understood backwards – but we must live it forwards.  Looking back, you can always see exactly when you should have bought and sold your shares.  But don't be fooled into thinking you're able to see in real time exactly when to do it.  In financial markets, hindsight is always clear, but foresight is legally blind.  Consequently, for most investors, timing the market is practically and emotionally impossible."

Benjamin Graham