Doctors cannot guarantee that they will never make mistakes or miss a serious illness despite their best efforts because they are human and prone to errors. It is important for them to acknowledge their limitations and strive for continuous improvement in their practice.
Doctors are under immense pressure to never miss a serious illness, but it is not realistic to assume they will never make a mistake. With a shortage of GPs, the weight of responsibility on doctors is even greater, and the pressure to perform perfectly is harmful.
The similarity between being a GP and a hairdresser is just like being a "really hardcore hairdresser." Being a GP can be compared to being a "shit hairdresser."