The lesson that I have learnt is to not only buy the dip, but to buy it slowly.

Keep a stash of funds set aside whilst prices are bullish. When it dips, don't panic into using up all your spare funds at once. Drip them in as the market declines. Then you can sell on the way back up again.

But it's hard for investors to keep a spare "pot" of funds. They want a return on money, not to let it sit there.

I guess it's the age old Optimist vs Pessimist viewpoint as to how you want to work your own strategy.