A repair sometimes needs the old screw that looked too ordinary to save.

Importance is contextual and cannot be judged at the moment of throwing away. A screw is completely undistinguished until the exact hour when it is the only one of its kind left in the house, and nothing about it announced that in advance. Sorting by apparent significance is a poor filter, because significance gets decided later by a break you have not had yet.

Keep a small box of dull things: fixings, spare parts, the odd cable. Apply the same to notes, contacts and half-learned skills, which behave identically. The rule is not to keep everything, only to stop assuming unremarkable means useless.