Seneca explains why the Stoic practice of negative visualization (premeditatio malorum) is so valuable - it reduces the shock and devastation of difficult events by mentally preparing us for their possibility. When we've already considered how we might handle job loss, illness, or relationship problems, these challenges become less overwhelming if they actually occur. This isn't pessimism but psychological preparation, similar to how fire drills make real emergencies less chaotic. By reducing the element of surprise, we can respond with greater composure and effectiveness when real difficulties arise.