What does it mean that processing means deciding what to do with each item?

Every piece of information needs a decision — act on it, store it, or discard it.

Example: You open your email and see 40 new messages. You read the first one — a request from a colleague — think 'I should reply to that,' and move to the next. You read a newsletter, think 'interesting,' and move on. You read a shipping notification, think 'okay,' and move on. Thirty minutes later you have read all 40 messages. None of them have been answered, filed, or deleted. You have consumed information without processing it. Tomorrow morning, you will re-read most of these messages and repeat the cycle. Processing would mean making a decision on each one the first time: reply now, schedule a reply, file for reference, or delete. Reading is not processing. Deciding is.

Try this: Choose one inbox — email, physical mail, a notes app, a read-it-later queue, whatever has the most accumulated items. Set a timer for 25 minutes. Go through each item top to bottom and make exactly one decision per item: act on it now (if it takes less than two minutes), schedule a specific time to act on it, file it in a reference system, or delete it. Do not skip any item. Do not say 'I will decide later.' The decision must happen now, even if the action happens later. When the timer ends, count how many items you processed. Notice how different this feels from simply reading through the same list.