Habit ...

'Alas, of all enemies, habit is perhaps the most cunning, and above all it is cunning enough never to let itself be seen, because the person who sees the habit is saved from the habit. Habit is not like other enemies that one sees and against which one aggressively defends oneself; the struggle is actually with oneself in getting to see it ... Sometimes a person becomes aware, as when a dream flashes by and is forgotten, that habit has changed him; he wants to make amends but does not know where he should go to buy new oil to rekindle his love. Then he becomes despondent, annoyed, weary of himself, weary of his love, weary of its being as paltry as it is, weary of not being able to get it changed, because unfortunately he had not in good time paid attention to eternity's change and now has even lost the capacity to endure the cure.'

—K, XVI.36.

'Of all sophists, time is the most dangerous, and of all dangerous sophists, habit is the most cunning. It is already difficult enough to realise that one changes little by little over the years, but the fraud of habit is that one is the same, unchanged, that one says the same thing, unchanged, and yet is very changed and yet says it, very changed.'

—K, XVII.315.