[Hookbill the Goomba]

Originally Posted by Inziladun

Morgoth may have led Túrin to a path of destruction, but it was Túrin who chose to follow it.

I agree. Character flaws are always a great contributor to the ultimate downfall of the tragic figure. In Steerpike's case it was also his pride and arrogance that lead him to be discovered and his plans be overturned.
This desire for prowess and need for more seems to be a prominent factor in both. Many times Turin is gifted the opportunity to settle down and not go after his doom, but each time, when a new danger arises, he straps on his sword and goes out. One of the most poignant points in CoH for me were the scenes just before Turin decides to face the Dragon. Níniel tries to disuade him, but Turin goes all the same. First when the Orcs are invading;

But ehrn tidings of the coming of the Orcs were first brought to Ephel Brandir, he [Turin] did not go forth and yielded to the prayers of Níniel. For she said: 'Our homes are not yet assailed as your word was. It is said that the Orcs are not many and Dorlas told me that before you came such affrays were seldom, and the woodmen held them off.'
But the woodment were worsted, for these Orcs were of a fell breed, fierce and cunning; and indeed they came with a purpose to invade Brethil, not as before passing through its eaves on other errands or hunting in small bands...
...
Therefore Turambar arose, and took up again his sword Gurthang and he went to battle.

Later when the Dragon himself comes...

Now Turambar was in haste to go; but when he came to Níniel to bid her farewell, she clung to him, weeping grievously. 'Go not forth, Turambar, I beg!' she said. 'Challenge not the shadow you have fled from! Nay, nay, flee still, and take me with you, far away!'
'Níniel most dear,' he answered, 'we cannot flee further, you and I. We are hemmed in this land. And even should I go, deserting the people that befriended us, I coulf not take you forth into the houseless wild, to your death and the death of our child... Take heart, Níniel. For I say to you: neither you nor I shall be slain by this Dragon, nor by any foes of the North.' Then Níniel ceased to weep and fell silent, but her kiss was cold as they parted.

Túrin does try to justify his decisions. But ultimately, it is, as Mnemosyne said, "you can't be entirely sure how much of the tragedy has to do with what he is (Hurin's son) or who he is."