The problem of missing the target.

Observing a bowman giving his demonstration at Warwick Castle I heard him call the arrow which missed the target a “sinner”.
Once in Norway when I stepped over the boundary marker into a private garden I became a “trespasser”. In fact the older I get the more I am conscious of sin within myself and one Bible verse is a constant challenge for it states that the person who “knows to do good and does not do it," to that person it is SIN. (James 4:17)

What is sin? It is missing the mark, it overstepping the mark, in fact it is not doing what is right.
The following footnotes are interesting, and instructive. It reports the literal meanings of the Hebrew and Greek words variously rendered "sin," "sinner," etc. They disclose the true nature of sin in its various manifestations.

What SIN IS:
(1) Transgression, an overstepping of the law, the divine boundary between good and evil.
(Psalm. 51:1 Romans 2:23)
(2) Iniquity, an act inherently wrong, whether expressly forbidden or not (Romans 1 :21-23)
(3) Error, a departure from what is right (Romans 1:18; 1 John 3:4)
(4) Missing the mark, a failure to meet the divine standard (Romans 3:23)
(5) Trespass, the intrusion of self-will into the sphere of divine authority (Ephesians 2: 1)
(6) Lawlessness or spiritual anarchy (1 Timothy 1:9)
(7) Unbelief, or an insult to the divine veracity John 16:9).

More about SIN.
(I) Originated with Satan (Isaiah 14:12-14)
(2) Entered the world through Adam (Romans 5: 12)
(3) Was, and is, universal, Christ alone excepted. (Romans 3:23; I Peter 2:22)
(4) Incurs the penalties of spiritual and physical death (Genesis 2:17, 3:19; Ezekiel 18:4-20; Romans 6:23)
(5) Has no remedy but in the sacrificial death of Christ (Acts 4:12; Hebrews 9-26) availed of by faith (Acts 13:38-39).

So to summarize, sin is an act, the violation of living in obedience to the revealed will of God.
It is a state, the absence of righteousness and also a nature of enmity toward God

Christians can sin in thought, word, action, inaction, and small faith.
But praise God there is forgiveness and cleansing, from Him - see Proverbs 28:13; 1 John 1:9. The old nature wars against the new nature of the believer - see Galatians. 5: 17. But the believer is helped to obey God's instructions, by the Holy Spirit of God, who fills those who are yielded.