When people are confident of their next paycheck, they have a predisposition to buy most of their “because I want it” items that are within financial reach (and maybe even just out of reach as well – hence the credit card). That’s because their psychic pain threshold for buying is just above their actual expendable income level.
Here’s how to visualize it: there are usually, say, 5-7 “extra-budgetary” purchases a person might have in mind for the next two months or so: nicer sunglasses, or an expensive wireless mouse, or shoes or some type of clothing, etc. And most of those things will actually get purchased within a rolling 2-3 month time frame, without the buyer feeling that any of them represent a considered purchase – even if the sunglasses or shoes might be in or above the $150 range.