The same power of memory that can heal a person can also poison them. It depends entirely on which past you choose to revisit, and how. The science is clear about this double edge, and the wilderness wanderings of ancient Israel show both edges at work in the same people.

Mental time travel is one of memory’s great gifts, and it cuts both ways. Scholar of memory Charan Ranganath points out in his 2024 book Why We Remember that returning to the past can lift us or sink us, depending on which memories we dwell on and how we frame them. Nostalgia, that bittersweet pull toward earlier days, can warm a lonely heart, and it can also leave a lonely person lonelier, measuring a thin present against a glowing past that may never have been so golden. Its darker cousin is rumination, the habit of circling the same wounds again and again, which deepens the groove of pain while leading nowhere. The faculty is the same in every case. Aimed one way it brings gratitude and strength. Aimed another it breeds resentment and despair.

He points to a further twist. Nostalgia tends to gild the past, smoothing off its hardships and brightening its pleasures, so the remembered version glows warmer than the real one ever did. That glow is harmless when it warms us toward gratitude. It turns dangerous when it makes a former bondage look like home.

What decides the outcome is the choice of which past to rehearse.