That essentially used to be the case at the dawn of antibiotics when someone was septic and they took some penicillin and went from (accurately) feeling like they were about to die to feeling dramatically better but still needing to continue the course to adequately clear the infection from the bloodstream. Now if you’re septic you’ll get pumped full of IV Augmentin in a hospital and ramp it up from there if it’s not clearing, you don’t get the option of deciding to stop early.

Modern medical evidence points to the importance of always finishing your antibiotic course to be a myth that leads to unnecessary extended antibiotic exposure.