I've asked other bass players what was the song that, when they started out, they never thought they could play. And then one day they finally figured out how to play well and then knew they could actually play bass. For me it was Old Brown Shoe by the Beatles. I learned exclusively on Beatles songs and that one always seemed like a Holy Grail of bass songs. I figured I would never learn it or be able to play it. I did finally learn it and now it seems so easy to me. It opened my eyes to the fact that I could learn any bass song. Any other stories?