Seed of Lust
Usually each sin is an outcome of a smaller sin. One of the vivid examples is the forbidden look which according to Prophet Jesus (AS) is the seed of lust. His Eminence told to his disciples:
Avoid from looking at haraam, for indeed it is the seed of lust and the cause of sin.
إیّاکم و النظر إلی المحذورات. فإنّها بذر الشهوات و نبات الفسق
?: Misbah al-Shari’ah, Ch. Ghadh Basar