The lifeguard you never noticed was watching the water the whole time you weren’t.

Safety is mostly somebody else’s sustained attention. For two hours a person scanned the same water in the same pattern, mostly bored, so that the one moment that might matter would not be missed. Nothing happening is the successful outcome of that job, which means it looks like sitting in a chair. Your not thinking about drowning was the service.

Say something on the way out, because almost nobody does and the work is dull. Then notice where else this applies in your day: crossings, kitchens, buses, locked doors. Thanking one person who guards something is a decent habit to start, and it takes a sentence.