The 90-day rule in minimalism dictates that when decluttering, you should only keep hold of things that you have used in the past 90 days, or will use in the next 90. This allows you to keep hold of seasonal items while singling out those that you promised yourself you would use but never touched. It can be a hard but useful exercise to try if you are finding it difficult to let go of items you are worried you will need again in the future. If you haven't used it by now and have no plan to, you likely don’t need it.