Source: Probably movie!verse RotK [Dunharrow]
Disclaimer: This is Tolkien’s – Kortirion likes to play in the sand-pit.
He’d long ago taught himself to sleep on demand, but tonight precious sleep refused to come. He stared at the canvas overhead. ‘Did he really have the strength? He was a man, men were weak – how many times had he heard that whispered in corners in Imladris? But Lord Elrond trusted him... Arwen loved him... Gandalf, his old friend, told him that this was his destiny. But was he weak? Like Isildur was weak? Did he have the strength of the olden kings they said he resembled?
Finally, he remembered other words ‘...my Captain ...my King’ and reassured, he slept.