Do you think that becoming a brilliant artist, music composer, writer...

I think many a brilliant mind can be a bit eccentric or at least appear that way. Creativity is like unleashing a part of your soul for all to see. Many would never do that. Perhaps very creative people have exceptional courage.

Insanity sounds harsh. I think Seneca's madness means the passion, the craziness, the weirdness-the uniqueness-what makes a great genius special

Same. When I write poetry, stories, or song lyrics, I'm either depressed, angry, emotionally numb, or just plain insane. This usually results in whatever I'm writing to not only be in-depth, but also pretty dark and gloomy.

That seems to be how it works for a lot of people !