1 Corinthians 8:10
“For if a man see you who hast knowledge, sitting at meat in an idol's temple, will not his conscience if he is weak, be emboldened to eat things sacrificed to idols?”
After having said, “Take heed lest this your liberty become a stumbling-block,” he explains how and in what manner it becomes so: and he continually employs the term “weakness,” that the mischief may not be thought to arise from the nature of the thing, nor demons appear formidable. As thus: “At present,” says he, “a man is on the point of withdrawing himself entirely from all idols; but when he sees you fond of loitering about them, he takes the circumstance for a recommendation and abides there himself also. So that not only his weakness, but also your ill-timed behavior, helps to further the plot against him; for it is you who make him weaker.”
Source: Homilies on First Corinthians (New Advent)