Being a pacifist and a positive idealist, Albert Einstein didn't want to accept the existence of Black Holes - even though he knew better.
It was not unreasonable for
Einstein opted to not accept the existence of black holes
because factual evidence of it had yet to be uncovered.
Black dwarf stars also exist theoretically but has yet to be
detected and in all likelihood hasn't come into existence yet.
Nonetheless astrophysicists could accept its eventual existence
with confidence in an era when our knowledge of the scope of
the universe has greatly expanded since Einstein's time when
the Milky Way was the only known galaxy in the universe. And it
is probably true that black holes did not exist in the early stage
of the universe. Einstein made his 'mistake' because he was
ahead of his time.