We pay attention. We react to the situation at hand. We anticipate problems. Because we don't know the right answers in advance, we find ways to come up with the answers on the fly. Think about this the next time you're merging onto a busy freeway.
Testers are like executives.
I don't send a tester on a complex exploratory mission until that tester has gained credibility on the easier missions. The tester must show an ability to design a good test strategy, execute good tests, find important problems, and report them in a compelling way. Furthermore, the tester must be able to explain his work. Only under those conditions do I come to trust that tester's work. Remember it's the skill of the tester, the social system of the project team, and the testing situation at any given moment that enables excellent exploratory testing.