Why Did Galadriel Warn Legolas to Beware of the Sea?

"If thou hearest the cry of the gull on the shore, thy heart shall then rest in the forest no more."

In The Silmarillion, there is a beautiful myth about the awakening of the Elves. The Elves were not exactly made; they were awakened from a deep sleep by Eru Ilúvatar (God) near the bay of Cuivienen.

“Many waters flowed down thither from heights in the east, and the first sound that was heard by the Elves was the sound of water falling over stone.”

The fi…