Nu’man bin Bashir relates: I heard Allah’s Messenger ﷺas having said this (and Nu’man pointed his fingers towards the ears): What is lawful is evident and what is unlawful is evident, and in between them are the things doubtful which many people do not know. So he who guards against doubtful things keeps his religion and honour blameless, and he who indulges in doubtful things indulges in fact in unlawful things, just as a shepherd who pastures his animals round a preserve will soon pasture them in it. Beware, every king has a preserve, and the things God has declared unlawful are His preserves. Beware, in the body there is a piece of flesh; if it is sound, the whole body is sound, and if it is corrupt, the whole body is corrupt, and listen it is the heart.
(Sahih Muslim)
Allah has defined the things which are lawful and those which are unlawful. In between these there lie certain things which are doubtful. The person who avoids the use of such things guards himself against falling into pitfalls. For the use of doubtful things paves the way for falling into the net of evil.
At the outset no one dares commit glaring evils; he starts from the acts which have no evil around them, but the intention behind them is no good. He then proceeds slowly and steadily, and most of the time unconsciously, on this dangerous path without realising the enormity of danger lying ahead, and ultimately falls victim to evil.