Story - How to find one?

I have found the seed of many stories that I have written in
1)a dramatic incident that I came across
2)a situation where I don't see eye to eye with others
3)a character that I found interesting

But these give just a seed of the story. Not the entire story. You have to use your imagination to flesh out the story.

Let me cite an example. This happened quiet a long time back, when I was in school. It was in chennai.

I was waiting for the train to go to my school. The train , when it came,was crowded. A boy, vegetable basket in his head, was the first one to alight. He jumped out even before the train stopped. He ran swiftly to the other side of the platform, to catch the other train that was about in the opposite direction. Half way through, he suddenly swerved trying to avoid the invisible pursuer. But it was too late. The police man, out of nowhere, swooped on him and caught him by the collar. It is illegal to hawk in railway station. The boy tried to free himself in vain. But he couldn't shake off the police.

I didn't see anymore. I had to catch my train. But what I saw, it has stayed with me still.

I am convinced that what I saw can give rise to a story. But I am yet to find one.

I can make the boy flee the police and board the running train. That would be a happy ending.
The boy can flee and board the train. But in the melee the vegetable basket falls on the platform ruining all his investment. That would be a tragic ending.
The boy flees and boards the train. He throws couple of cabbages at the police on the platform. 'Wasn't this what you wanted?' he shouts as the train speeds away. That would be a bitter sweet ending.

I am not happy with any of the above. But I am confident I will find the right story.