Example? The one we were just discussing! Doctors have convinced the government to make medicine a licensed profession, so they got the government to use force

Example? The one we were just discussing! Doctors have convinced the government to make medicine a licensed profession, so they got the government to use force on their behalf to stop you attending to someone's ailment. There's no legal block to you creating your own company to compete with TSMC or Apple or Google, yet, you won't be able to do it. The sheer amount of effort it needs to compete makes it impractical. Entry barriers are usually created by the effectiveness of the incumbents and lack of any way to get customers when you're the worst option.