Every restoration has a lifespan. Placing one starts a clock: it will need replacing, and the replacement will be larger than the original, and so will the one after that. The first filling in a tooth is the beginning of a sequence, and the sequence only runs one way.
Which means the decision not to treat is not a passive act. It is a treatment decision with a measurable long-term value, and it deserves the same diagnostic rigour as any other.
Watching is a plan
An early lesion that is not progressing is better monitored than filled. That requires a record precise enough to detect change — measurements, imaging at sensible intervals, the same operator looking at the same numbers over years.
Without that record, 'watch and wait' is guesswork, and a dentist who cannot measure will always be tempted to treat.