If you were to lie in bed for two weeks straight without getting up, you would need a physical therapist to teach you how to walk again. The muscles that control your walking would stop working with just two weeks of non-use.
So what do you think happens when you haven’t been using your brain?
When you actually need it for an idea or to solve a challenge, it’s not ready. Your brain is just like your jump shot, your troops if you’re the head of an army, the chain on your bicycle: It gets rusty if it’s been sitting on the bench for too long.
Read books. Listen to personal development audio. Talk to someone smarter than you and learn what they know (by asking questions). Get and keep your brain in game shape.