Doubting ourselves is one way the adversary takes advantage of us. Don’t let him. Defend your divinity by tuning him out and remembering you’re a son or daughter of a King who loves you no matter what.
Satan gets a better grip on us each time we think poorly of ourselves. If we allow him the pleasure of taking away our individual worth, we grant him the power to essentially take over our lives and direct our paths.
He wants us to think we're not good enough to progress eternally when we commit sins, no matter the size. He wants us to sink so low that we cannot pick ourselves back up. He wants us to let him win. 
Whether you're going through a particularly hard time in your life or you're just struggling with a simple trial, remember the worth of souls is great in the sight of God.