Is destiny fixed or variable?

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I have always wondered whether what happens to us fixed i.e. prewritten as presumed by some faiths or whether we make our own destiny and too what extent one can change ones destiny. I for one feel that destiny can be prewritten at the time of our birth because that would mean that if I do somethign wrong I was supposed to do it according to destiny hence I m not wrong on the whole.But if it variable to what extent. I beleive that destinies are fixed to some extent but with potential of variability i.e. one's final goal may be fixed but the means of achieving it will differ and it is these choices that will decide our furher destiny. what is your opinion?