A strange idea becomes useful after the right problem finally meets it.

An idea’s usefulness is not a property it carries alone. It appears when the idea meets a situation shaped to receive it, and until then the idea can only look eccentric. Plenty of what you have set aside was not wrong, just unmatched.

Keep the odd ideas somewhere you will actually revisit rather than discarding them. When a hard problem arrives, read that list before reaching for the conventional approach. Some of what has been sitting there for a year will suddenly look like it was written for the situation in front of you.