When people take antibiotic and end up without finished the course and continue doing it, it create resistance of that antibiotic. The bacteria get chance to protecting its new generation against that antibiotic. And next level that antibiotic do not work on that patient. The consultant suggest for new antibiotic for that patient. Thus resistance of antibiotic keep increasing if end up without finished course and taking it irregularly . The last level is no more antibiotic work on that patient.