I imagine David felt like he had a lot of disadvantages. He was small and always getting left behind. He was a lowly shepherd while his brothers had the opportunity to serve in glorious battles. Even his father didn't think of David when Samuel came to look over the sons of Jesse in order to pick the new king. Yes, if anyone had disadvantages, it was David.
But God has a way of turning our disadvantages into advantages. When David went out to fight Goliath, he didn't try to fight him like a soldier would. He didn't grab a sword and shield. In fact, he rejected them. Instead, he went out to face Goliath as a shepherd would face a threat. He armed himself with a shepherd's weapon: a sling. Who else would have thought of such a thing? Certainly not a man trained for war. Yet with David's disadvantage, he was able to bring down the giant that no one else would dare to face.
When looking at your disadvantages today, take heart. God has a way of using things that seem bad to us to bring about something that is good. The Bible is full of stories that relate the truth of that. Don't wallow in pity over your disadvantages. Just be open to the Lord, and allow Him to use you however He may see fit. Who knows? He may use you to bring down another giant.
And we know that all things work together for good to them that love God, to them who are the called according to his purpose. - Romans 8:28