I described the ways ideas/interests work for me the other day using the metaphor of a beetle, expanded below:

I encounter ideas as if they were eggs of some insect laid in the substrate of my mind. Someone else's idea beetles wander through my mental environment, lay eggs, and move on.

If the conditions are favourable to them, then they hatch into larvae and wiggle around – this is the initial active interest phase. Then they pupate; they become dormant. They can stay in this phase for days, weeks, or longer; it is at this point they can also seemingly die and enter the hobby graveyard, I can't tell if they're alive or dead until they eclose or rot away. 

When, if, they emerge from their cocoon, there are two actions they can take: fly away or settle in. Idea beetles that fly away are things that I were interested in for a while but ultimately I extracted everything I wanted from them and no longer really care about - e.g. frognoise music. Idea beetles that settle in may be more or less active over time, wiggling and digging tunnels and resting, but essentially become long-term (special?) interests - e.g. My Immortal, Paradise Lost, foraging. 

It's not like the beetles that leave have no effect - going through the entire process of larvae, pupa, adult leaves marks, tunnels, etc. This affects the way that beetles that stay behave; the reason I regularly buy music on bandcamp is because I followed a rabbit trail about a specific subniche of noise music that I ultimately decided I didn't like.

How do you conceptualise your mental idea space?