What does it mean that priority systems prevent reactive living?

Without a priority system you respond to whatever is loudest rather than what matters most.

Example: You sit down Monday morning with a clear intention to work on your product strategy — the project that could reshape your next two years. Before you open the document, you check email. A client has a question that will take five minutes. A colleague needs feedback on a deck by noon. Your manager forwarded an article with "thoughts?" in the subject line. An hour later you have answered the email, started the deck feedback, skimmed the article, and opened three browser tabs you cannot explain. The strategy document is untouched. Nothing that consumed your morning was unimportant. But none of it was the most important thing. You did not choose those tasks — they chose you, by virtue of being louder, more immediate, and easier to start than the work that actually matters. This is reactive living: a day shaped by incoming signals rather than outgoing intention. A priority system would have told you, before the inbox opened, that the strategy work comes first — and given you structural permission to delay everything else.

Try this: Track your next full workday in two columns. In the left column, log every task you work on and when you started it. In the right column, note what triggered you to start: was it a notification, an email, a request from someone, an internal feeling of anxiety, or a deliberate decision based on what matters most? At the end of the day, count the ratio. How many tasks were triggered externally versus chosen deliberately? If more than half your day was externally triggered, you are living reactively — and no amount of productivity technique will fix it until you install a system that decides what comes first before the triggers arrive.