Every
electron in the universe is
exactly identical to every
other electron. It's not just that
we can't tell them apart,
nature itself can not tell the difference (this has
observable
consequences in physics). Not only that, the description of a
positron moving forward in
time is identical to the description of
an electron moving backward in time.
This led Richard P. Feynman to suggest that there is only one electron
in the universe moving back and forth in time, so the reason that all
electrons are indistinguishable is that they are in fact all the
same electron.
(I should note that Feynman did not mean this terribly seriously,
but it illustrates as forcefully as anyone can that electrons are
completely identical.)