Nu‘man bin Bashir relates: I heard Allah’s Messenger ﷺ as having said this (and Nu‘man pointed towards his ears with the fingers): 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 hearken it is the heart.
(Sahih Muslim)
Allah has clearly defined the things which are lawful and unlawful. Every person has a clear knowledge of them. But in between the two, there are certain things which are doubtful.
The man who shuns the use of such things guards himself against pitfalls, since the use of doubtful things paves the way to evil. At the outset no one dares commit glaring evils; he starts from the acts which apparently have no evil around them, but the intention behind them is not good. He then proceeds slowly and steadily on this dangerous path without realising the enormity of danger lying ahead and ultimately falls victim to evil.