We like to think of ourselves as in control when it comes to what we'll shell out: A budget is a hard line, and there's a point where "guilty pleasure" becomes "too much to justify." The truth is something trickier, though. We're way more flexible on how much we'll pay — and it's all because of what we were just looking at.
Scientists at New York University have published research showing that shoppers adjust their valuations of products simply because of how items they've recently encountered are priced. Browsing a lot of lower-value goods can influence the decision to pay more for something we spot just after. Meanwhile, we might hold back on something that's reasonably priced if we've just spent time looking at higher-value items.
Think of it like the money version of this optical illusion, in which both orange circles are the same size. Our brains interpret the world in a dynamic way, which saves our skin more often than it harms us. By creating context about value, we can adjust our resources and expectations. But that also means we can trick ourselves into spending too much, or holding off on something we might actually need or want.
For people who like shopping, part of the pleasure comes from stumbling on a perfect find and making an exception for it. But if you tend to justify purchasing or not purchasing certain items on the regular, give yourself some objective facts. Do your research on price points and keep your findings handy. If that thing you want seems like too much (or too good to be true), you'll have a quick and easy way to ground yourself and actually think things through.