Full Idea
It makes no sense to say I could have been someone else, yet Counterpart Theory implies not merely that I could have been distinct from myself, but that I would have been distinct from myself had things gone differently in even the most miniscule detail.
Gist of Idea
Counterpart Theory absurdly says I would be someone else if things went differently
Source
Alvin Plantinga (Transworld Identity or worldbound Individuals? [1973], II)
Book Reference
'The Possible and the Actual', ed/tr. Loux,Michael J. [Cornell 1979], p.163
A Reaction
A counterpart doesn't appear to be 'me being distinct from myself'. We have to combine counterparts over possible worlds with perdurance over time. I am a 'worm' of time-slices. Anything not in that worm is not strictly me.