To put it in Biblical terms? Grace is not static, it is dynamic and belongs to God. Faith is also dynamic, always in action (ref Acts of the Apostles). The only way I know someone can "lose" Grace is to deny the Power of God's Grace to save. If someone denies His Grace, then they never trusted in Him in the first place and never knew Him.
If we believe our actions count one jot or tittle towards salvation then it is no longer Grace.
I know the next question so will answer it. Does this give 'motivation' for someone in God's Grace to sin as they see fit? As Paul says in Romans "May it NEVER be!" By Grace through faith we establish the Law.
Grace is not static, it is dynamic and belongs to God.
If it belongs to God, why can't he take it away? If you see evidence that that has happened, why would you conclude it was never there in the first place?
Grace is a gift. It's not only dynamic, it's alive. In fact, it's Alive.
But like any living thing, you can kill it, or more accurately, evict it. (I don't like the verb "lose". When I lose something, I never do it deliberately. It is impossible to "lose" grace any way except deliberately.)
There's a riposte to this that is illogical. It goes, "If I can throw it away by my actions, it was never a gift to begin with!" That doesn't make sense in any context. If I give you a new Cadillac, and you wrap it around a tree, does the fact that you've wrecked your Caddy make it no longer a gift? Of course not.
That bad news is that it also doesn't obligate me to give you another new Cadillac. Even if you apologize to me and beg for a new one, it's probably not going to happen.
God, while certainly not obligated, is happily far more generous than I am.