Ah. So all of Christ's statement about no one plucking his sheep out of his hand rests, not on God, not on Christ being the Good Shepherd, but on the willingness of the sheep to follow him. Do you recall the parable of the lost sheep? The sheep was lost because it wasn't following the shepherd. But, you know, the shepherd left all of his other sheep in search of the one that had wandered off. Why? Well, among other things, because it was his sheep that had got lost. He didn't go out looking for someone else's sheep, did he? No. It was because the lost sheep was his own sheep that he went out to find it.
It seems, though, that you believe that the lost sheep, having failed to follow the Shepherd, wandering off as sheep are naturally prone to do, has thereby plucked itself out of membership in the Good Shepherd's fold and is no longer one of his sheep. If so, if this is how Jesus looks at the wandering child of God, why would he go after him/her? Shepherds don't go off in search of strange sheep; they've got their own flock to care for, after all.
A sheep that has wandered off into the wilderness, away from its shepherd, is more or less helpless, vulnerable, not just to predators, but to entanglement in vegetation, or drowning in water, or stumbling into a crevice, or just growing its wool coat so big that it can't function, dying of immobility and the killing starvation and thirst that result. And finding its way back to its shepherd is, essentially, impossible for a sheep that has wandered out of sight of him. They are bizarrely - and dangerously - ill-equipped for survival in the wild. But, even so, you would place the responsibility for remaining within the Good Shepherd's flock on the sheep.
"No one" necessarily includes everyone. The Good Shepherd's sheep have been given to him by God, and identify themselves by following him, but they remain Christ's "sheep" because no one has the power - not even the sheep themselves - to remove any of them from his hand. And this is a crucially important thing given how much like actual sheep we are in our relationship to our Good Shepherd.