Why I don't mentally prepare for the future: When whatever-it-is happens, I will be a different person. Therefore, I cannot 'prepare' for future calamity or even difficulty in any meaningful way, aside from the general principles of prudent planning, precaution, fostering detachment from the world, and God-reliance. The person I am today will be gone tomorrow. If I try and prepare today's me for tomorrow, I might indeed be well prepared, but it's today's me who is well prepared, and a new version of me will wake up tomorrow, entirely unprepared, and have to start afresh with eschewing self and seeking to rely on God.