The Lord's Perception Is What Matters
The plans of the heart belong to man, but the answer of the tongue is from the Lord. All the ways of a man are pure in his own eyes,but the Lord weighs the spirit. (Proverbs 16:1-2 ESV)
Proverbs 16 verses 1 and 2 are talking about our own view of how holy or righteous we are. These verses warn against this as God will be the one to determine our holiness.
Just because we don't think our sin, is a sin, this doesn't mean it's not a sin. We cannot 'lean on our own understanding' of ourselves. Proverbs 3:5-6 states "Trust in the Lord with all your heart, and do not lean on your own understanding. In all your ways acknowledge him, and he will make straight your paths."
It is the Lord's perception that matters, not ours or anyone else's. We can think or perceive that we are holy but it's God that ultimately decides how holy we are. This can also go the other way where we may not think we are holy or righteous but God does. This is why we cannot rely on our perceptions of ourselves. Some may view themselves too highly while others not high enough. We should strive to see ourselves the way God does. (His children whom He loves dearly and who was created to have a unique and special relationship with Him)
Apart from God, holiness is impossible and this is the reason we need the Holy Spirit. In order for the Holy Spirit to indwell us, we need to have a personal relationship with Jesus Christ (be born again by accepting Jesus as our Lord and Savior). Once the Holy Spirit has in-dwelled us, the Holy Spirit will start to make us more Christ-like, but only if we submit to Him. We cannot make ourselves holy on our own.
Living a holy life will allow God to shine through us as we will be set apart from the rest of the world. He can't shine through us when we look and act like the world. Why would the world want what they already have? If we are set apart and shine brightly with love, acceptance and joy even through the hard-times, don't you think more people would want to come to know Christ?
Here is a link to an article if you're interested more in how to live a holy life: https://www.gotquestions.org/holy-life.html