Bob Dylan is without question one of the most famous musicians of all time. A poet as much as he was a musician, Dylan is celebrated for being a civil-rights activist either directly or indirectly for the way in which many of his songs resonated with the political discourse that was taking place in the and 60's.
So why on earth would a large crowd of his own fans, at a festival he was headlining, boo this icon that for many of them was a musical hero?
The year was 1965
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The answer isn't blowing in the wind, it is in that picture above. Bob committed the horrible act of musical treason when he dared play an electric guitar. Up until 1965 point Bob had never done so on an album or in a live performance and some of his old-school fans were not pleased about the transition.
This is just another example of people not being willing to "transition with the times" and I have been guilty of figuratively "booing" many bands that did precisely that... This is most evident in how I constantly berate Metallica for "selling out" with the release of their wildly popular but significantly toned down Black Album.
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The guitar that was used in that performance got "lost" on a plane and disappeared for nearly 50 years. According the the pilot who found it, Dylan's management was contacted about how they wanted him to return the Stratocaster but management never got back to him. I can only presume that this is because Dylan probably has 50 of these and they are likely provided for free by Fender anyway. Little did they know that this guitar would end up becoming one of the most valuable musical relics of all time as it fetched $965,000 at an auction in 2013.
In a real dick move, Dylan's attorneys tried to sue for the guitar, but it was settled out of court and the details are not available to the public. This guitar sale narrowly beat out the previous record of $959,000, which was for a guitar belonging to Eric Clapton.
While I definitely think it is up to Bob about what he wants to do there is no denying that moving over to electric was definitely a stark change to what people were accustomed to with his musical style. The dude can do what he wants but the fact remains that his most influential and famous work was certainly done on an acoustic.