Kent Nagano, writes Joshua Kosman, is one of the top 10-20 conductors in the world. So why is he still conducting the Berkeley Symphony – a community orchestra – after 25 years? “Nagano’s dedication to the BSO has occasionally had a far more concrete impact on his activities. Because of a scheduling conflict with a Berkeley concert, he says, he had to turn down an invitation to make his first appearance with the Berlin Philharmonic – not once, but four times before he finally debuted with the orchestra in 1997.”