Snowball or Thermostat?

Test whether a deviation amplifies itself or recruits its own correction.

Your credit card balance crept up 200 dollars last month. You are not sure whether to panic. Sometimes a bump like this quietly corrects itself, because seeing the statement makes you spend less next month. Other times a bump grows, because carrying a balance normalizes carrying a balance, and interest piles on. The right response depends entirely on which kind of bump this is.

Snowball or Thermostat? is a fast classification test for any deviation from normal. The cue is noticing something has drifted off its usual level, in either direction. The operation: ask whether the deviation amplifies itself (each turn makes the next turn bigger, like a snowball) or recruits its own correction (the deviation triggers a response that pushes it back, like a thermostat). Trace one concrete consequence of the deviation and ask if it feeds the deviation or fights it. If it is a snowball, act early, because it gets more expensive to stop. If it is a thermostat, you can often leave it alone and let the correction work. Do not run this test as a substitute for evidence; a plausible story about amplification is a hypothesis to check, not a verdict.