Some memories become precious precisely because nobody knew to document them.

Documented moments get preserved as records, which is a different thing from being remembered. Undocumented ones survive only in you, shaped by feeling rather than by evidence, and that is exactly what gives them their weight. Nobody knew to record them because nobody knew yet what they were.

This is a reason to be present rather than to photograph more. The moments worth keeping are usually identified afterward, so the only reliable preparation is to actually be there while they happen.