"Momentum investors are like the surfers we watch from beaches along the Pacific coast. Both must catch a wave. Both attempt to ride it as it breaks. But the ability to glide away smoothly before being caught inside the inevitable crash(ing wave) that follows is what determines success."

http://www.etf.com/sections/features-and-news/how-not-wipe-out-momentum?nopaging=1

You have to remain humble, especially when things are going well because no one knows what’s going to happen or how long success will last.

looking at charts, it's not what you look at that matters, it's what you see, and what does it mean to you, and what are you going to do about it

Nassim Taleb, of “Black Swan” fame, was asked, “What are the biggest risks out there right now?” He replied:

The fact that the world, as a result of quantitative easing, has seen an asset inflation that benefited the uber-rich, and that nothing has been cured. One cannot cure debt with debt, by transferring from private to public sectors. The markets will ultimately crash again, although this time it will hurt a lot more people.