A mindful quotation from René Descartes, Meditations on First Philosophy (Source)
“So in future, if I want to discover any certainty, I must withhold my assent ￼from these former beliefs just as carefully as I withhold it from obvious falsehoods.
It isn’t enough merely to have noticed this, though; I must make an effort to remember it. My old familiar opinions keep coming back, and against my will they capture my belief. It is as though they had a right to a place in my belief-system as a result of long occupation and the law of custom. These habitual opinions of mine are indeed highly probable; although they are in a sense doubtful, as I have shown, it is more reasonable to believe than to deny them. But if I go on viewing them in that light I shall never get out of the habit of confidently assenting to them.
To conquer that habit, therefore, I had better switch right around and pretend (for a while) that these former opinions of mine are utterly false and imaginary. I shall do this until I have something to counter-balance the weight of old opinion, and the distorting influence of habit no longer prevents me from judging correctly.
However far I go in my distrustful attitude, no actual harm will come of it, because my project won’t affect how I act, but only how I go about acquiring knowledge.
Like a prisoner who dreams that he is free, starts to suspect that it is merely a dream, and wants to go on dreaming rather than waking up, so I am content to slide back into my old opinions;
I fear being shaken out of them because I am afraid that my peaceful sleep may be followed by hard labour when I wake, and that I shall have to struggle not in the light but in the imprisoning darkness of the problems I have raised.”