Bai Juyi was already a celebrated scholar when he was sent into exile, and the verse catches him at the river's edge listening to a stranger's pipa, weeping at music he had no hand in making. The stick borrows that scene as a mirror for your studies right now. You're somewhere that feels like a detour from the path you thought you were on, whether that's a subject you can't seem to crack, an exam result that didn't match the hours you put in, or a programme that turned out harder and lonelier than the brochure suggested. The verse doesn't promise you'll be rescued from this stretch. It reflects back that the stretch itself is doing something to you that easier terms wouldn't.
Notice that Bai Juyi's white hair isn't framed as defeat in the poem; it's framed as proof of having lived through something. Your version of that might be the notebook full of corrections, the third re-read of a chapter that finally clicked, the quiet hour after everyone else logged off the study group. The stick is asking you to look at what this difficult season is teaching you that a smooth one couldn't, and to stop measuring yourself only against the version of you who expected things to go faster.