We make simple errors, such as confusing two similar sounding medications. We make complex errors, like omitting an important consideration from our differential diagnosis. Other times these errors cause trivial harm, such as an unneeded x-ray. Sometimes the harm is serious. Most of the time, though, medical errors are more or less harmful.
All doctors make errors.
Some doctors may err more than others, but there is no such thing as an error-free doctor. Error-free performance is not compatible with human limitations. If doctors were routinely executed for errors, no physician would be left standing. Neither onerous punishment, nor unrelenting education, will eliminate medical error. We have always had medical error, but it is likely that errors are now becoming more common.