About Those Miraculous Moments...

        I've told you before that a good writer turns up the heat on his hero, and puts him in a perilous situation, right?  Suspense and conflict swirl around our protagonist, keep us on the edge of our seat, and make us wonder how he'll ever get out alive.  His enemies or problems should be worse than he is good, so that the odds are stacked strongly against him.  In fact, the opposition should be almost insurmountable.  That way, when he finally does defeat the foe, it's a much more satisfying victory.
        But here's where many beginning writers trip up:  They've allowed their hero to get into a dreadful mess (good job), but they haven't figured out how to save him realistically (oops).  So, out of nowhere, an inheritance arrives to save the house.  Or a helicopter appears in the desert sky to rescue him just as the vultures are circling.  Or his boss dies and he gets the promotion after all.  Or his girlfriend suddenly turns into a superspy.  These miraculous saves are doing the opposite to your story: They're killing it. 
        No bit of good fortune should be large enough to save the day, ever.  This makes for a cheap ending (like a hideous dream sequence where you realize you've been duped the entire time) and readers will resent you and mutter, "How convenient," among other things.
         So here's the rule on luck:  You can have outrageously bad luck happen, but not outrageously good.  If your hero is about to play in the Superbowl but suddenly a rhinocerous escapes from the zoo enclosure, charges into him and breaks the hero's leg-- as utterly stupid and impossible as that may be-- a reader or moviegoer will actually accept that before he'll accept an equally unlikely scenario that helps your hero.
        And we've all seen it and accepted it when the girl running from a kidnapper finds a gun, but it has no bullets in it, right?  Nevermind that every day in the news you're reading about a kid finding a gun and accidentally shooting his grandmother with it, this one-- to work in your story-- must be unloaded.  And then she somehow escapes the house, darts through a dark forest and makes it to the highway-- but flags down her kidnapper's team.  What are the odds, right?  It couldn't be a housewife or a farmer heading down the highway, nope-- she will flag down the one car that keeps her in peril. People accept these kinds of wild flukes.  But it's because they're counting on you to deliver a clever, well-constructed save.  Don't let them down.