It introduced me to the idea that 'is' should be treated very carefully. Any assertion outside of strict formal languages that use it are half-truths at best. It also introduces heightens the emotional tone of a discussion. If you say "John is foo" you tend to create the impression that John will always and has always been foo. Foo-ness is a taint on his soul. Contrast that with reformulations that make it explicit that John's foo-ness is a fleeting association related to both his present situation, your current perception of it and the current socially accepted meaning of foo along with all it's implied baggage.
It introduced me to the idea that 'is' should be treated very carefully. Any assertion outside of strict formal languages that use it are half-truths at best. It also introduces heightens the emotional tone of a discussion. If you say "John is foo" you tend to create the impression that John will always and has always been foo. Foo-ness is a taint on his soul. Contrast that with reformulations that make it explicit that John's foo-ness is a fleeting association related to both his present situation, your current perception of it and the current socially accepted meaning of foo along with all it's implied baggage.
I realise I might be rather off-topic :-)