Why is bacterial antibiotic resistance a major health concern?

Bacteria live almost everywhere. Our body can co-exist with many kinds called 'healthy bacteria', while we can also fight off many unhealthy bacteria and maintain our well being with our normal immune system. When a bacteria develops resistance to antibiotics; often because it is exposed to an antibiotic but not enough to completely kill it off -- like when someone takes some of their medicine, but doesn't finish it because they start to feel better, or because it is a very common bacteria and antibiotic soap is used all the time until a bacteria comes along or changes so that it can resist it, then our system has a much harder time killing it off and the options we have for treating it become fewer and fewer. Flesh eating disease is one example of a bacteria that has become antibiotic resistant. Many people die or become horribly disfigured by the spread of resistant bacteria before their system overcomes it, or a suitable treatment is found.