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Not sure if it is his originally or it is borrowed ....
I've heard this idea before, perhaps worded differently. Not an original concept, but to your friend, it might be.
There's no wrong or right answer. You can't tell people they "shouldn't" feel a certain way. Well, you can, but it's kinda like teaching a pig to sing. So, if someone thinks, or wants to justify, that their playing is born from their depression, hard times, heartbreak, etc. ..... hey, more power to 'em. If they can take a negative, and turn it into a positive, that's a good thing. We are, after all, made up of the sum of our experiences.
Now, if someone was to say, "you can't play the blues, unless you've lived the blues" .... to me, that kinda smacks of elitism. For it starts to qualify the human experience. Rate it. The ol' "my hard luck is deeper than yours" .... doesn't make anyones blues any more valid than anyone else.
How many anti-war songs (or songs describing the horrors of war) are actually written by combat veterans? Few. But many great songs exist. Judging someone's "soul" .... everyone's got an opinion, right?