What's My Pebble?

Let's reconsider the biblical story:  Be it true or not, let's take it's metaphorical value!
The Philistines were at war with the Israelites.  The Philistines represented evil while the Israelites counted as the armies of God.  Amongst the Philistines there was a nine foot giant who, for forty consecutive days, would come to the top of the hill overlooking the Israelite encampment, mocking their soldiers.  'Who amongst you will fight me?" he would shout.  They were all afraid of Goliath and chose to hide away rather than encounter certain death. 
David was a teenage messanger for King Saul and was bringing a message to the frontline one day when he heard the call of Goliath.  He couldn't understand why those amongst his own people were too frightened to answer.  David begged Saul to allow him to fight the giant.
No one believed that young David could slay Goliath, but after much persuasion he was allowed to go forward.  Against the armour and armory of the giant David's choice of weapon was a pebble and sling.  He took careful aim and released the pebble with ferocious power.  It flew through the air at such speed and with such accuracy that it bore a hole in the giant's forehead, rendering him senseless as he fell to the ground.  David then stood atop of Goliath and drove a sword through his heart.
Now, in my story, I am David!  The mortgage is Goliath.  So what's my pebble?  The wheels are turning.