You have a lot of reasons for resistant antibiotics. Some jobs push you to go to work when ill. If your kids got sick, some jobs weren't understanding. Then you have the brilliant folks who stop taking their meds, when they feel "better". Sometimes doctors have to make an educated guess, as to what is wrong with you. They will try one antibiotic, then another. I used to get allergies in the spring every year. It would almost always turn into a bad infection. Most antibiotics did not work on me. I finally found one that did work, so they always prescribed that one. Now it may not be on your "preferred drug list", or some thing like that. I have tried 3-4 antibiotics in a row before, trying to get one of those infections knocked out. Now I get less sick with seasonal allergies, but I have it almost year round. (vs. VERY sick for a shorter time) Regardless, if the antibiotic doesn't kill what it was intended to kill, it will develop immunity over time. That is why they cannot depend on the tried and true. They have to keep coming up with new ones. Dogs... Remember Frontline working like a charm, and then it didn't? Those fleas got immunity. Rats also become immune to poison over time. I hope we never get to where these things no longer work. Pre-antibiotic history will show that even things we consider minor now, could turn out really bad for you.