Limiting One's Involvement in Worldly Concerns - Middah Miyut Derech Eretz
"The former generations made the study of Torah their regular concern and their daily work their occasional concern, and they succeeded in the one and in the other. The recent generations have made their daily work their regular concern and their study of Torah their occasional concern, and they have succeeded neither in the one nor in the other." (Babylonian Talmud 35b)