According to Professor Ahmed Ibrahim, as he stated in his book علم أصول الفقه, precedent/assumption (الاستصحاب) is defined as considering something valid if it has previously been ruled so. The word also means assumption of continuity.
As an example of precedent/assumption, Professor Ibrahim mentions the assumption of ownership of an asset being traded. The trade is assumed valid until proof is shown that the seller did not own the asset at the time of the trade.
However, Professor Ibrahim emphasizes, ignorance of the law is no excuse for violating it. Claiming assumption here is not accepted as a valid defense.
He then tells of a famous juristic rule, "Assumption/precedent is a deduction method for refutation, not for affirmation."
I can see that there are many issues where this method can come in handy, but how can it be better defined? For instance, the Church has ruled 2000 years ago that Trinity is the cornerstone of Christianity. Do we then accept that based on precedent? The first few pages of the Quran chastise people who simply follow their ancestors, culture or peers without applying their reasoning faculties. It is quite possible, therefore, that a precedent is established and assumed valid for centuries but it is false or flawed if one would actually scrutinize it. I humbly say that the abrogation issue is the best example of such.
A candle loses nothing by lighting another candle.