I’ve stopped expecting improvement during each practice/playing session. Playing a musical instrument relies on cumulative effort and I realize that “day by day, I’m getting stronger in every way.”
Daily effort is important in all worthy goals/missions, but that effort needs to be deliberate. Deliberate practice is structures and each playing session is begun with a set of goals. Throughout practice I test things out. Dr. Noa Kageyama of bulletproofmusician.com has an excellent article on what deliberate practice is and isn’t.