Do oil paintings have to be thick?

This is unnecessary. Oil painting also has a thin painting method, which is a painting method with more volatile oil. There are also thick paintings, pigments piled up and fresh colors; Thick painting is the texture effect of pigments mixed many times, such as the texture of a big sweater. The traditional easel oil painting pays attention to production, which is thin in the dark and thick in the bright. I can't explain this clearly in a few words, but I can understand some subtle things by drawing a little more.