Why do Pilots keep Logbooks?

Pilot Log Book

A Pilot Logbook is a record of a pilot’s flying hours. It contains every flight a pilot has flown, including flight time, number of landings, and types of instrument approaches made. Pilots also log simulator time, as it counts towards training. Pilots are often required to show proof of their aviation experience when applying for a new Pilot Job.
In most countries, pilots are required to maintain a logbook, per their government’s aviation regulations. The primary purpose is to show that certain requirements have been met for a certificate or rating, and for currency purposes.
Pilots also keep a log of their hours for personal reasons, they log special moments, memorable flights, and it is a momento of a long successful career upon retirement.