What does it mean that every thought has a shelf life?

Example: An engineering lead recognizes an architectural insight during morning standup — something about how the caching layer could eliminate three downstream race conditions. She's presenting, so she doesn't write it down. By afternoon, she remembers she had an insight about the caching layer. By the next morning, she remembers she had an insight. The specifics — the precise connection between the cache invalidation pattern and the race conditions — are gone. The thought had a shelf life of minutes. She gave it hours.

Try this: Open a blank page. Write down 10 thoughts you've had in the last 48 hours — anything from a task you need to do, to an idea about a project, to a personal realization. Next to each one, assign a shelf life: minutes (fleeting insight, contextual connection), hours (action item, meeting takeaway), days (a developing opinion, a project direction), or permanent (a principle, a reference fact, a core value). Notice the distribution. Most people discover that 60-70% of their thoughts have a shelf life of hours or less — and that their capture systems are designed for the 30% that lasts days or longer.