Many of our advances have come in a slow grind, through hard work and hard research, blood, sweat and toil. This is not that. This is when an idea hits you like a lightning bolt, fully or mostly formed.
In ancient times, this was said to be the work of beings called muses. (In Christianity, this is the purpose of the Holy Spirit, just in case you were wondering what exactly that guy did all day besides be something of a third wheel to the Father and Son, like the 1992 Dream Team including Michael Jordan, Larry Bird, Magic Johnson, Patrick Ewing, Karl Malone, John Stockton... and Christian Laettner. Who, for the record, was chosen over Shaquille O'Neal.) Even today, we use the term 'muse' to refer to whatever the stimulus is when something like this happens. Whatever inspires you, that's your muse.
This is Step 1.
Anyone who's had this happen- and hopefully that's just about everyone- has probably experienced, though not quite thought much about outside of the act, Step 2: recording that inspiration. An idea that you come across through the slow grind, while difficult to obtain, is by the time you get what you need fairly well ground into your head. An out-of-nowhere visit from a muse, however, is fleeting and fragile. There is as of yet nothing in your head for that inspiration to hang onto. Once it leaves the forefront of your mind, there is every chance that the idea will recede right back into the depths from whence it came, never to return. Even if you can recall it, it is not easy, and what you dig back up might look nothing like the idea that originally struck you.
And any idea that hopes to make an impact on the world around you cannot make that impact until and unless it survives the journey from your mind into said world.
This is why some people, upon being hit with an idea out of the blue, are gripped with a sudden urge to get the idea recorded somewhere, anywhere, while they still have it, and keep it at the forefront of their minds at all costs until they can. Write it down. Turn on a tape recorder. Turn on a webcam. Blog it. Something. Anything, quickly, before the idea is gone forever. In fact, this is the recommended thing to do; this Michigan State course syllabus, for example, says not to worry if the idea doesn't sound pitch-perfect. You have an idea. Unless the idea is utterly abhorrent, don't worry if it's not perfect. You can give it closer analysis later. That's Step 3. You're still on Step 2: get the idea down.
Some of your more creative types don't even wait for a free moment. They just abruptly cut themselves loose from whatever it is they're doing, sleep included, and get it down somewhere.
Once a place to record the idea has been found, the idea must still be actually recorded. And because you're not out of the woods until that has happened, this part of the process can easily become all-consuming. No external stimuli. The world is shut out. There is only a pen, paper, and a semi-frantic scramble to indulge whatever has gripped the mind of the inspired.
And it's not enough sometimes to get some of the idea down and come back later. Though when an idea for a blog post comes up at work, due to limited break time, I've gotten a sort of system down where I get down what I can, make it to a point where I can leave off and, through what I've written down, be reminded of what I'm supposed to write at the next opportunity. By writing down a certain part of a thought, I can remind myself of the rest of that thought. That might not work for you, though, and it doesn't always work out for me. For some people, they either record everything, or risk losing their inspiration halfway through the recording process.
It can happen to the best. Samuel Taylor Coleridge, as he claimed, was struck with the entirety of the poem Kubla Khan in 1797, reportedly in an opium haze. Not a recommended source of inspiration, but hey, it worked for him. As he told it, upon waking from the haze, he immediately set about composing the poem, intended at 200-300 lines, but only 30 lines in, he got a knock on the door from "a man from Porlock". The two talked for an hour, after which he resumed writing. But in that hour, he'd lost it. He scrambled to reconstruct the poem, but petered out at 54 lines. The rest was simply gone. When reading Kubla Khan, the first 30 lines and the last 24 seem disconnected from each other. The man from Porlock isn't a universally believed explanation- theories range from it being an excuse for the two halves of the poem being so different from each other to the possibility that he got stuck, with the inspiration not even waiting the hour to abandon him.
Whatever happened, lines 37-47, coming after the break, read like so:
A damsel with a dulcimer
In a vision once I saw:
It was an Abyssinian maid,
And on her dulcimer she played,
Singing of Mount Abora.
Could I revive within me
Her symphony and song,
To such a deep delight 'twould win me,
That with music loud and long,
I would build that dome in air,
That sunny dome! those caves of ice!
This reads to a lot of people like Coleridge raging against the heavens, trying to recall lost inspiration, almost pleading for it to return. If he could only remember the rest of that poem, he'd put together the best damn writing you ever saw.
The 1954 movie On The Waterfront put it another way: "I coulda had class. I coulda been a contender. I coulda been somebody." Which is one of the most frustrating, exasperating thoughts a person can have.
Don't let that thought happen to you.