It's the old garbage in, garbage out principle. If we fill our minds with Philippians 4:8 kinds of thoughts...thoughts that are true, pure, and of good report...then our actions will naturally follow the trail blazed by our thoughts. So every thought does matter. Jerry Bridges once said, “The deceit of the mind is carried on by degrees, little by little. We are first drawn away from watchfulness, then from obedience." No sincere believer sets out each day with the intent of ruining their life by some great sin. But when we fall, it is usually because little by little, bit by bit we lowered the discipline of our minds. So think on these things which are of good report, Paul says. It will purify your worship and fill your life with the peace of God.