Driving a black cab in London was a difficult achievement for about 100 years. I don't know whether the Knowledge is as important any more. Since you lived in London, you know how obscure addresses can be there. It's not like Costa Rica where they don't have addresses at all for the most part, but it's certainly not straight forward like most American grid cities. My wife grew up at 2 Vawdrey Close. A cabbie would know that's off Cleveland Way, between Mile End and Cephas Street in Tower Hamlets. The rest of us would never find it, even with a map, unless we knew where to look. The Stepney Green tube stop was very close. Bethnel Green was a bit farther, but close enough. We spent time there in the 1980s for the most part. When we moved to Seattle, it got a whole lot harder to get to London, and impossible once we had a kid. By the time we could get there again, my wife's family had moved to Hornchurch. They have all left London by now.