The melody of Should’ve Known Better by Richard Marx runs 337 notes across 63 bars, 5:16 long in Fm at 120 beats per minute. The tab sits low on the neck, mostly under the fourth fret, one note at a time — no chords to barre and no strumming pattern to keep up with. A piano backing track plays the chords and bass underneath, so the line you are learning sounds like the record even at half speed.
Prefer to strum and sing it instead? Should’ve Known Better chords and lyrics.