I do not think that all who choose wrong roads perish; but their rescue consists in being put back on the right road. A sum can be put right: but only by going back till you find the error and working it afresh from that point, never by simply going on. Evil can be undone, but it cannot 'develop' into good. Time does not heal it. The spell must be unwound, bit by bit, 'with backward mutters of dissevering power'* ... or else not. It is still 'either-or'. If we insist on keeping Hell (or even Earth) we shall not see Heaven: if we accept Heaven we shall not be able to retain even the smallest and most intimate souvenirs of Hell.
C.S. Lewis, The Great Divorce, Preface (1946)
*this line is a quotation from Comus by John Milton (line 814)