Rule 2 of 33 · Chapter I — How We Communicate
Match the medium to the urgency
Why this rule exists
Most of what we send each other is not urgent, but we have trained ourselves to treat every ping like a fire alarm, and that reflex is expensive. A message in a channel is a note on a shelf; the reader gets to it when they surface. A direct mention is a tap on the shoulder. A phone call or a page is a hand grabbing your arm. When we blur these, everything starts to feel like an interruption, and the genuinely urgent thing drowns in a sea of things that could have waited until after lunch. The medium is a promise about response time, and when the promise is honest, people can trust the quiet channels enough to actually go heads-down. A team that can't tell the difference between 'whenever' and 'now' ends up context-switching all day and calls it collaboration.
In practice
Ask yourself when you actually need a response before you pick how to send it. If it can wait until tomorrow, put it in a channel with no @-mention and move on. If you need someone specific this afternoon, mention them and say so plainly, including a deadline. Reserve calls and phone-level urgency for things that are genuinely blocking or genuinely time-sensitive, and say why up front. When you do need someone now, it's kind to lead with the ask instead of 'you around?' followed by three minutes of silence. And if something isn't urgent, resist the pull to make it feel urgent just to jump the queue.
When it doesn't apply
Incidents override all of this; when production is down, grab whatever attention you need however you need to. And people new to the team should over-signal until they've calibrated, because it's better to check in too eagerly than to sit blocked in silence for a day.