P is for parallel
S is for serial

Ideas tend to pop up in large quantities when we are brainstorming.
Ideas appear in a very parallel way. One idea gives rise to another and so on until we get tired or decide to stop.
The whole idea generation process is very parallel and produces a lot of results in a short time frame.

When we are trying to change a good idea into reality, the process is very different.
What needs to happen is a sequence of steps, one after one, in a very serial way. There is not much room for doing multiple actions at the same time. Actions need to happen in a sequence. That's why it usually takes much longer to realize an idea than it takes to come up with the idea in the first place. Provided that you come up with an idea, of course.

Time requirement contrast between idea generation and idea realization is main reason for a known saying that success is 20% inspiration and 80% perspiration (good old hard work). Of course, provided that you are able to come up with good ideas.

P is for parallel = inspiration = 20% of time
S is for serial  = perspiration/hard work = 80% of time

P.S. Is it just the opposite with value distribution: 80% of value is in inspiration and 20% of value is in perspiration?