There is a strange mercy in imagining, on an ordinary day, that you have already lost what you love most. Not to wallow, and not to brace for the worst, but because the mind has a quiet habit that robs every life: it stops seeing whatever it has grown used to. Picturing the loss, briefly and on purpose, makes the thing visible again.
The practice
Praemeditatio malorum, the premeditation of adversity, is the deliberate rehearsal of loss, difficulty, or failure before any of it arrives. You imagine the plan falling through, the journey going wrong, the people you love no longer here. You hold it clearly for a moment, and then you return to a present that is suddenly, vividly intact. Seneca practised it not to spoil his days but to stop sleepwalking through them.
"We suffer more often in imagination than in reality." — Seneca
Running the treadmill backwards
This is the Stoic answer to a trap the mind sets for everyone: we adapt to whatever we have. The first morning in a new home you notice every window; a year later you notice none of them. Psychology has a name for the mechanism, the hedonic treadmill, and a good deal of evidence that it flattens almost every gain back to a baseline of wanting more. Negative visualisation runs that treadmill backwards. By picturing a thing gone, you feel its presence again, and gratitude returns with it. Gratitude is little more than clear sight of what is already enough. It is the deliberate cousin of contentment (Santosha): the peace that comes from noticing you already have what you need.