I see a strong parallel between creativity and gardening. Like a fruit, growing from seed to ripe, ideas do the same.
Idea seeds are those vague, half-formed thoughts that quietly appear in your mental space. They occupy a strange state where you are aware of them, but would struggle to write them down or explain to someone else coherently. That is the defining characteristic of an idea which is not mature yet.
Slightly more mature ideas are in the growth phase. They form of the idea has started to emerge, and you can half-express it, but there might be logical errors as you still haven’t fully thought it through yet.
Ripe ideas are fully developed and can be coherently expressed with the fewest words necessary.
Ideas can grow along this path explicitly or implicitly. You can explicitly grow ideas by sitting down and trying to write them. Or they can grow implicitly in the background as you live your life and expose yourself to experiences and other ideas.
Sitting down to write an idea is like trying to harvest it. It’s easiest and works best when the idea is ripe — the idea will almost pour out of your brain onto the page in this case. If you try to harvest an idea before it’s ripe, it will be harder.
The analogy might break down slightly here. With ideas, the act of trying to harvest them actually accelerates their journey towards ripeness. Trying to express an idea forces you to understand it better and clarify it. This is one way of growing an idea: the explicit way.
Ideas can also grow implicitly. They can quietly sit on your mental back burner as you live your life and expose yourself to experiences and other ideas. Maybe another idea acts as a bee that pollinates the first idea and together they form a complete, ripe idea. But in order for them to be able to safely sit on the back burner as long as it takes, they should be still captured in some kind of way, or else you’ll probably forget them.
Note that an idea’s state of being written down vs in head, and public vs private are each orthogonal qualities. Ripe ideas aren’t the only ones that can be written down and published. Idea seeds can still be attempted to be written down (although it will be hard), and also published.