It's hard to beat the nagging feeling that there MUST be some way to predict when to buy into the market and when to sell. The feeling persists despite all the actual evidence to the contrary. I'm a professional who knows the truth from the data and my experience, yet the feeling persists because I have a human problem. 

Gazing from the current summit I wonder if the next step will take us to greater heights or start a march down from this most delicious vista. 

Unfortunately it's human nature to feel more pain from losses than pleasure from gains.

When that nagging feeling occasionally rears its head, I deal with it using the discipline of 4 easy habits:

1. Remember the risk of missing the one or two best performing days of the year

2. Rebalancing back to my asset allocation strategy. 

3. Dollar cost averaging into the market with new cash or for major portfolio shifts. 

4. Turning off the news and taking a walk to enjoy the beauty around me.