[quote=@Shadow Dragon]
<Snipped quote by Legend>

Why not? Is it an moral reason, or a physical/magical reason?
[/quote]

If I go back again, I will disrupt this timeline so that it diverges, meaning that the very moment I go to the past again will be disturbed. The feedback loop will cause such a great divergence from my original timeline that I'll disappear instantly, with or without the Strings of Fate. You can consider it a time paradox, though those don't really exist.