Imagine that you arrive at the scene of an accident, and find a smashed car at the bottom of the cliff on which you are standing. The car is green, and with very large wheels and tyres – the sort you’d only find on customised cars. At the cliff edge you see the green paint on many of the rocks, and the large distinctive tyre tracks leading over the edge of the cliff. The soil was disturbed, and rocks had fallen away. Directly below were the remains of the vehicle. Logically speaking the car had slipped over the cliff. Although you were not present, and do not necessarily understand how it had happened, all the evidence  (secondary factors) points to one logical conclusion: the car went over the cliff.