I'm paraphrasing, but I can only imagine that's what David was thinking as he volunteered to kill this giant.
34 But David said to Saul, “Your servant used to keep his father’s sheep, and when a lion or a bear came and took a lamb out of the flock, 35 I went out after it and struck it, and delivered the lamb from its mouth; and when it arose against me, I caught it by its beard, and struck and killed it.36 Your servant has killed both lion and bear; and this uncircumcised Philistine will be like one of them, seeing he has defied the armies of the living God.” 37 Moreover David said, “The Lord, who delivered me from the paw of the lion and from the paw of the bear, He will deliver me from the hand of this Philistine.” 1 Samuel 17: 34-37 (NKJV)
David could rely on past experience - with my hand I have killed lions and bears. It didn't have to be exact, just similar.
David also had faith in God - the Lord who delivered me from lions and bears will deliver me from this giant.
Experience and faith are great things to rely on while job hunting. I'm using my experience to show that what I've done in the past can be done in the future though there may be a greater challenge. The greater challenge is where the faith comes in and I'm relying on that also.
The beauty of experience is that when you're in a situation that appears challenging to others, you have the fortitude and wherewithal to execute successfully. Your methods may astound others or may appear unorthodox, but they are successful. As you keep slaying giants, you can become an expert giant killer.
Have you killed any giants recently, based on past experience?