Imagine you're organizing a surprise party (a transaction) that needs to happen precisely at 5 PM (the commit time). However, all your friends (the database nodes) have slightly different watches, and you can't trust them to be perfectly synchronized. To avoid the surprise being ruined by someone arriving early or late, you decide to use a special app (TrueTime) that allows everyone to agree on a time window when 5 PM will definitely occur, say between 4:59 PM and 5:01 PM.
You tell your friends to be ready and in position anytime within that window, but the surprise will only start exactly at 5 PM, as determined by the app. Because of the app's accuracy, you're confident that no one will act before 4:59 PM or after 5:01 PM, and since everyone prepares in advance, the party kicks off flawlessly at 5 PM without further coordination needed. This is akin to how Spanner uses TrueTime to set a global commit timestamp that ensures all