how the fate is responsible for the tragedy of oedipus?

I think the idea of fate can't really be seperated from the concept of free will. A central theme of the Oedipus the King is the tension between individual action and fate. While free choices, such as Oedipus’s decision to pursue knowledge of his identity, are significant, fate is responsible for Oedipus’s incest and many of the other most critical and devastating events of the play. By elevating the importance of fate, Sophocles suggests that characters cannot be fully responsible for their actions. It becomes difficult, for example, to blame Oedipus for marrying mother given his ignorance.

Consider this quote,

TEIRESIAS

Well, it will come what will, though I be mute.

OEDIPUS

Since come it must, thy duty is to tell me.

TEIRESIAS

I have no more to say; storm as thou willst,

And give the rein to all thy pent-up rage. (341-347)

Teiresias insists that, regardless of what he says or does, fate will play itself out.

The gods declared what would happen to Oedipus, and so it did. If it didn't, the gods would be shown to be fallible, i.e. not worthy of man's worship.

oedipus tried to avoid his fate.when he comes to know that he will murder his father and marry his own moter he leaves corinth and comes to thabes.in this way he tried his best to avoid what was told by oracle