The most practical rule to avoid impulse buys during flash sales is simple: wait 24–72 hours before deciding. Flash sales are engineered to create urgency; the pressure to 'act now' bypasses rational cost-benefit thinking. A short cooling-off period interrupts the emotional surge and lets you test whether desire survives a little delay. During the wait, ask practical questions: Will I still want this after 48 hours? Do I already own something that serves this purpose? Is the true unit cost reasonable given how often I'll use it? Often the sale's emotional energy fades and the purchase decision becomes clearer. The 24–72 hour window is short enough that most deals don't disappear immediately but long enough for reflection.

Make this rule operational by adding two low-friction tactics: (1) add the item to a curated 'consider' list — a dedicated shopping list or wishlist — and remove it from immediate checkout; (2) set a calendar reminder to reconsider at the end of the cooling-off period. If you still want it, compare return and refund policies (some flash items have stricter returns) and proceed with confidence. For higher-value items, lengthen the cooling-off period. The goal is not to never buy on sale; it's to avoid purchases driven purely by manipulated urgency. Treat the cooling-off rule as a habit that preserves both your money and your sanity.