A discount is a story about the seller’s old price, not about your situation. Thirty percent off tells you what someone decided to charge last month; it says nothing about whether the thing is worth buying today, at this price, with this money. Separating those two questions is most of what makes a purchase feel good a year later.
The test that works is boring: what would you pay for this item if there were no sale tag at all? Write that number down before looking at the discount. If the sale price is below your number, the deal is real. If the sale price is above it, you have found a cheaper version of something you did not want at that price.
Then check the cost of ownership rather than the sticker. Filters, cases, batteries, subscriptions, maintenance and the energy it uses are part of the price, and they are often where a cheap purchase becomes an expensive one. A device that is twenty percent cheaper and needs a proprietary consumable every two months is not cheaper.
Finally, give the decision a short delay and a single comparison. One competing option and one night of sleep remove most buyer’s remorse without turning every purchase into research. A good deal survives both; an urgent deal usually does not, which is exactly why it is presented as urgent.
