"في اللحظة التي أتوقف فيها عن المتعة به، سأكون قد انتهيت منه."

Simplified Meaning:

When someone says they'll stop doing something once it stops being enjoyable, they're saying that fun and happiness are the reasons they're doing it in the first place. Imagine a person who loves painting. They paint because it makes them feel good and creative. But if one day painting starts to feel like a boring chore or makes them unhappy, they'd put down the brush and quit. It's like a child playing a game - they keep playing because it's fun, but if the game stops being enjoyable, they would stop playing right away. This idea can be applied to work or hobbies; if you're not enjoying your job or hobby anymore, it might be time to think about making a change. This approach helps ensure you spend your time on things that make you happy.