[Mithadan]

It was the inherent nature of Elves that they loved the lands where they lived and sought to foster and preserve them. As such, it was also part of their nature to wish to fix the ills done to the world by Morgoth, though this was too great a role for them to perform.

Because all else passes them by and departs, while they live on, Elvish "immortality" is a great burden as well as a blessing. As a result, Elves experience enduring sadness concerning things long gone and regret for misdeeds and choices made. It may also be that slights or offenses that a man would forget in due course are also long recalled by Elves and are the sources of resentment. However, with long life comes also some measure of wisdom to temper such ill-feelings.

Many of the poor decisions made by Elves were not well or long considered. The rebellion of the Noldor, though perhaps fostered by the long influence of Morgoth's webs of lies and deceipt, was a quick choice triggered by the Darkening of Valinor, the theft of the Silmarils and the murder of their king. It was a decision made in a days time. Maeglin's treachery, though prompted by his desire for Idril and hatred for Tuor, was likewise a rapid choice made under the unimaginable pressure of Morgoth's interrogation.

Elvish longetivity no doubt factors into these misdeeds but is not the root cause.