What is declinism (the "things were better in the old days" bias)?

The tendency to see the past in a positive light and the future in a negative one — to believe society is in decline.

The mechanism is partly memory (we remember the good and forget the bad of earlier times — see the fading of negative affect) and partly negativity bias applied to the present and future, where ongoing problems are vivid while progress is gradual and unnoticed. Every generation tends to believe its own era is uniquely going downhill.

Example: "Kids today have no respect and everything's falling apart" is a complaint recorded in nearly every era for thousands of years — which is a strong hint the feeling tracks a bias, not an actual unbroken multi-millennial decline.

Tip: Nostalgia is a poor measuring stick. When you sense things are "getting worse," check it against actual long-run data rather than the rosy glow of memory.