The more you try and think of something to write, the more it eludes you. It's extremely frustrating, when you feel the motivation to write and yet you stare at a blank page for what seems an age, and when you give up and walk away it hits you from the middle of nowhere. Of course, it can be at the most inconvenient of times.
In the middle of computing one day I got an a story whilst trying to learn something that would inevitably come up in my final exam. The thoughts come flooding in, completely distracting you from work. Luckily, I had a notebook handy and started multi-tasking. Learning and creating at the same time. By the end of it I had a plot, a group of characters and everything! I ended up titling it "A parent's nightmare" which you may have read from my old account.
At other times you come up with something and are unlucky enough to find you don't have anything to jot it down on. The creature of creativity is an elusive thing, and if you aren't prepared at all times you may find that it will jump out in front of you from the undergrowth, but then run off and hide again before you can get a good look at it. So I ended up taking a notebook EVERYWHERE with me, to school, friends houses, even cafe's or restaurants. I won't get caught out again!
Then you have the problem of - you have your no certainty it will lead to anything apart from a jumble of words on a single page. Or even a jumble of words stuck in your head! Sometimes you have to go in search of the creativity creature, net in hand and a tasty piece of bait to entice it with.
Most of the time you may need to take a leap of faith, and find that the creativity creature becomes curious and shyly steps forth to investigate the story you weave from your fingertips, but in the end - you never know if a story will be succesful until you show it to somebody else.