In the "Shuowen Jiezi" (Shuowen Jiezi), "tiǎn" is its original character. The "Changjian" (Changjian) states that this character is formed by the semantic combination of "tiān" (heaven) and "xīn" (heart). Applying the standards of heaven to one's heart, one often feels ashamed, which carries a meaning of self-restraint.