An example from Kant:

If you also find this too obscure - this plan which I offer as the Prolegomena to any future Metaphysics - bear in mind •that it’s not necessary for everyone to study metaphysics, •that many people have the aptitude to succeed very well in sciences (even deep ones) that are closer to sense-experience, yet cannot succeed in investigations dealing with highly abstract concepts, •that such people should employ their talents on other subjects; •that someone who undertakes to make judgments in metaphysics - let alone to construct a metaphysical system - must satisfy the demands I have made here, which he cannot do by rejecting them, so he must either adopt my solution or thoroughly refute it and put another in its place; and, finally, •that this notorious obscurity (·allegations of which are· often a cloak to cover the accuser’s laziness or stupidity) also has its uses ·as a defence against insolent intruders·: people who maintain a cautious silence in relation to other sciences approach metaphysics in a spirit of bold pronouncements and impudent decisions, because their ignorance is not here contrasted with the knowledge of others.