The unexpected kind gets all the attention — the windfall, the rebate, the cheque nobody saw coming. But look at what the expected kind actually did.
The same amount, on the same date, for four years running. That regularity is what let you sign a lease, plan a holiday eight months out, sleep on a Sunday night. Nobody celebrates a salary landing on time. It is the least dramatic event of the month, and it holds up most of the structure.
Both kinds are real. One of them is just very bad at being noticed.