Psychology says people who refuse to start a new notebook until the old one is completely finished may have a strong need for closure

Refusing to start a new notebook until the old one is finished may be about much more than stationery. It can reflect thrift, routine, organization, continuity or a desire to avoid waste. Psychologically, though, it may also provide a satisfying sense of closure that comes from completing what was started.

Raccontata daeconomictimes.indiatimes.com