>if a doctor is good enough, he can just start his own practice It depends. Many instruments, such as PET in nuclear medicine, cost a lot. One have to work for

>if a doctor is good enough, he can just start his own practice It depends. Many instruments, such as PET in nuclear medicine, cost a lot. One have to work for hospitals/networks to help his/her patients with that instruments, no matter how good he/her is.