What does it mean that signal requires a defined goal?

You cannot distinguish signal from noise without a defined goal. Without knowing what you are trying to achieve, every input carries equal weight — which means no input carries real weight.

Example: An engineering lead opens Slack on Monday morning and sees 47 unread messages. Without a defined goal for the week, they read all 47 — responding to requests, reacting to opinions, following tangential threads. Two hours vanish. A different lead with a clear goal — 'ship the auth migration by Thursday' — scans the same 47 messages in eight minutes, pulls three that relate to the migration, archives the rest. Same inbox. Radically different signal extraction.

Try this: Write down the single most important outcome you are trying to produce this week in one sentence. Now open your email, Slack, or RSS feed and scroll through the last 20 items. For each one, mark it S (signal — directly relevant to your stated outcome) or N (noise — not relevant). Count the ratio. If you did not have the sentence written down first, notice how much harder the sorting would be.