Both words give a similar message in context.

When I was an undergraduate student, I went to the epidemiology 1 class. The professor in charge of the subject was Professor Kwon Sook-il, who later served as the Minister of Science and Technology.

I went to the auditorium that day, and Professor Kwon said this.
"I went into a doctoral course, and one day my supervisor asked me to solve a complex equation. It was so complicated that I finally solved it for a few days and went to the lab, and he said, "Isn't the answer between this value and that value?" I asked because my answer was within that range. Did you give it to me as a homework and solve it separately? The professor asked me if I know the answer by solving it all perfectly. I can just roughly find it."

Professor Lee Joon-gyu said something similar when he entered graduate school. "A physicist must know the answer before making a calculation."

Both words give a similar message in context. Before calculating in detail and obtaining an answer with as much accuracy as possible, it is necessary to be able to guess the range of the answer through the loop calculation.

I'm not saying to calculate the compton scattering problem for graduate students in a complicated way and consider in detail what happens when an electron exits graphite, assuming that it is not stationary, to obtain a scattering formula. You won't be able to solve it by hand.

However, considering the ionization energy of carbon atoms or the work function of graphite, it is certain that the bound outermost electron can be liberated only by giving about 10 eV of energy. The initial momentum can be obtained by considering that the speed of electrons roam around in graphite, whether using Niels Bohr's hydrogen atom model or Fermi speed. Assuming that X-rays are also approximately 100 keV, the momentum of X-ray photons before scattering can be obtained.

In this way, the error rate can be obtained, whether the roughly wavelength change or the difference in the scattering angle with respect to the incident angle.

This is comparable to Fermi's assumption at the time that there were hundreds of piano orchestrators in Chicago. The ability to figure out that there are hundreds of people, not dozens or thousands. Students today will simply call the Chicago Piano Coordinator Association or search the Internet to find the answer. This is not inference. The ability to predict an answer through reasonable reasoning before calling or searching, which is actually a terrifying ability.

It is of paramount importance to develop this ability while studying physics. So, I told my students that if they study physics, they will have weapons as strong as missiles. Students laugh, but to be able to perform quantitative as well as qualitative analysis easily is an incredible ability. Moreover, it is most important to have the background knowledge to acquire all engineering knowledge faster than other engineering majors.

I always say that you can confidently say that it is a powerful weapon such as a missile, not a pistol or machine gun, so you can major in physics in your undergraduate years and then go to another department.

The professor of environmental engineering, who is working with me these days, did particle physics theory during his master's degree, but he said he couldn't actively major in physics. Of course, I responded that the undergraduate department can go to physics, and the graduate school can go to another field.

I have a professor of journalism and broadcasting and a professor who studies OTT in data science. It's possible because he's a physicist. He's a scholar who studies everything about the universe with interest.

It is outdated to think that physics only studies the momentum and energy of particles. Some only study classical research topics, while others go further.

I chose the humanities as my next research topic. Now I just need to find a like-minded humanities scholar. :)