Interesting point you brought up. Some people seem to argue that John is focusing on confessing every single sin that we commit as we commit them (keep a specific inventory) as an additional requirement to remain cleansed (1John 1:9) and if we forget a sin, we're toast!
Others would argue that John instead has in mind here a settled recognition and ongoing acknowledgment that one is a sinner in need of cleansing and forgiveness.
*Notice that verse 8 says, "If we say that we have no sin, we deceive ourselves, and the truth is not in us." Verse 10 says, "If we say that we have not sinned, we make Him a liar, and His word is not in us" and this is in CONTRAST TO - “if we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.”
If God does not require us to list and ask forgiveness for each and every sin, why would we keep bothering Him with specifics? If all we do is look backward, we can't see ahead of us to grow and move on.
Isa. 1:18 "Come now, and let us reason together, saith the LORD: though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool.
Isa. 43:25, 26 "I, even I, am he that blotteth out thy transgressions for mine own sake, and will not remember thy sins. Put me in remembrance: let us plead together: declare thou, that thou mayest be justified."
If God is willing to call us clean, shouldn't we be also?