For a great many people--leaders, songwriters, playwrights, astronauts, kings, little kids, the lonely, the sad-- dreams were powerful, unstoppable things.
They were a great deal like their maker.
Morpheus wasn't, at all, all-powerful, or even much better than a hyper-motivated mortal when he really got going, but a dream was nothing if not an idea, and ideas had more power than anything. Anything. He knew how to get things done.
He knew what to say, when to say it (usually), and how to say it to get through to people. He knew a lot more than most other gods gave him credit for.
If you get to weave dreams for people like Shakespeare, people like John Nash... didn't they think he learned something?
He considered his words carefully, and when Nanshe moved back, he stood a touch straighter, crossing his arms over his chest. He spoke to her with quiet intensity, and almost entirely without breaking her gaze.
... it wouldn't be me who was in your apartment.
"You threw it in my face once," he said. "You asked me how you could ever know I was being myself and not what you or anyone else wanted because of what my job is." He let that sit a second. "You tell me your not my Nanshe, as though you or she could ever be possessed. But what both you and she fail to realize that, when you dream and hope you see me--and I know you do that-- all you see are copies of me. I'm every face you see in a dream, but do you think that one gets every spec, every ounce of my consciousness?"
He searched her face, already knowing she was likely beginning to understand.
"I sincerely doubt there's anything anywhere that understands what you just said better than I do."
Unless a dreamer willed it, or unless he felt like seeing the person dreaming, Morpheus was everyone, yes. But he wasn't fully there. It wasn't fully him. If he was a soldier on Morrigan's field of battle, he remembered the plan of attack. If he was Erebos, he felt the depth of darkness inside him and everywhere around him. There was just something... Morpheus... about the copy. He was an excellent mimic.
But just a mimic.
"You've dreamt of me... thousands of times," he said. "A thousand copies. Even if I was pulling their strings."
"Did you love any of them any less?"
Are you sure?
The smile he gave her was conspiratorial and exceptionally charming.
"I wait for the day when you stop asking me that," he joked. "And yearn for it."