Whether a person has a theory has nothing to do with his personal practical experience. Theory serves practice, making people take fewer detours. But theory comes from practice, not fiction. This is materialist dialectics. So a person has no theoretical basis, but he has rich work experience. It is entirely possible to do good deeds in a down-to-earth manner, be good at summing up experience, and become a master in some aspects of work. You can also make building materials in your own field. This kind of person is very diligent. He kept learning in his work, constantly improving his quality and technical ability, and many people became experts. So you can't judge a book by its cover, and you can't forget such famous aphorisms.