If you don't invest with a very clear notion of underlying value, how do you do it?

"Long-term-oriented value investors have greater scope to produce superior risk-adjusted returns when the seas are rocky . The valid response when there's chop is to focus on the end destination —what value investors call intrinsic value—and not worry about whether the next wave is going to push the boat up or down . If you don't invest with a very clear notion of underlying value, how do you do it? Nothing else makes sense. Your ability to maintain focus on the long term comes from experience. You go through a couple cycles where every body else is screaming at you not to try to catch a falling knife, and then when you do so and make some money , it does wonders for you . . . and for your ability to do it next time. “

—Howard Marks, Oaktree Capital

If you don't invest with a very clear notion of underlying value, how do you do it?