I like card games, particularly Magic: the Gathering, because they're a nice mixture of strategy and luck. I don't like chess because it's pure strategy, and I don't like bingo because it's pure luck (this analogy is an oversimplification).
For a piece of fiction, how does a writer introduce an element of random circumstance without it ultimately seeming contrived?
Finding the sword of Godric Gryffindor would have been a DeM had the individual elements of that type of event not been introduced before hand.
Luke (a farm boy who has never flown a space ship) firing the killing shot at the Death Star is a DeM, except that the elements are introduced beforehand. (a. He's got the force, b. they have the plans, c. R2 probably helps out, d. he misses a few times, e. his buddy Han helps out too.)
Many solutions would be DeM except that all the pieces are introduced first in believable ways.
And that's how you do it. For the event you are considering, establish the points to the event before hand. It's a puzzle - you are writing a puzzle. Give all the pieces to the reader. Do it in a way that the reader doesn't necessarily see how they go together, except in hindsight. Then when you provide the solution, they smack their heads.
