Legolas first encountered death in Moria, when he saw Gandalf fall. He did not understand, at first - were not the Istari immortal? How could Gandalf really be gone? His insistence that it was not so was borne out, later, when the wizard returned.

His second experience came near Rauros falls, when he watched Boromir die. This time he was merely curious. Boromir was mortal, and mortals died. That was the way of it. But Legolas had never seen it happen before.

The third time, it was one of his own kind. He did not see Haldir of Lorien fall, but Aragorn assured him the elf had fought to the end.

That grief, more than the two others combined, nearly killed Legolas.