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And we do n't know what the future holds , just like we did n't know in Korea . Already we have a very large tail-to-tooth ratio . We are living in separate cities , but I flew out for a weekend visit . we implement a software virtual machine in a computing system ) , and we know how to use them , predict their behaviour , debug them when they go wrong , and apply them in solving real practical problems , nevertheless we do n't yet fully understand what 's going on . What he says about the Crusades demonstrates the difficulty Swinburne felt in coming to terms with the distinction he intuited between reality and its spiritual underpinnings : " To understand the crusades , " he insists , " we now think , we should be able to go back to their time : and when that was done , the loss of all later experience and of all analogy would perhaps have the fact actually occurring before our eyes as hard as ever to explain fully .