There are many reasons why antibiotics suck. One of them is because antibiotic-resistant bacteria are becoming more and more common as people use antibiotics incorrectly, often without knowing that they are potentially harming themselves.
Antibiotic-resistant bacteria (or superbugs) are bacteria that are resistant to antibiotics. They don't react to antibiotics and can survive even when a antibiotic is present. Paitients with an antibiotic-resistant strain of bacteria cannot use the same antibiotic that the superbug is resistant to, otherwise the antibiotic is ineffective against the bacteria. The bacteria can get resistance by getting a mutation that changes the bacteria slightly to have defend itself from the antibiotic. The other way is by "horizontal gene transfer." Bacteria that have resistant properties can share it with the bacteria that are nearby. If a bacteria that has resistance multiplies, its next generation has the same resistant properties. These bacteria can be transferred like others by food, water, and transport.