“for all have sinned and fall short of the glory of God,” (Standard Protestant Translation)
“for all have sinned and fall short of the expectation of God,” (Sensible Translation)
According to Liddell and Scott’s Intermediate Greek Lexicon (also called Middle Liddell) the word δόξα or δοξης can mean: expectation, an opinion, judgment, the opinion which others have of one, estimation, reputation, credit, honour, glory. (Its a secular lexicon, which is why its honest on this.)
See for yourself. http://www.perseus.tufts.edu/hopper/morph?l=do%2Fchs&la=greek#lexicon Click the link, then in the first entry, click “Middle Liddell.”
So the sin is not in failing to be as glorious as God, but in failing to meet up to God’s expectations for weak human beings.