“But he can also be incredibly sweet. And I know that, deep down, I mean the world to him." "Deep down? That sounds like settling to me. You shouldn't have to venture deep down in order to get to love.”

Henry J. Waters III (April 29, 2008) "The Tribune's View: The oil crisis - Shall we continue to fiddle?", Columbia Daily Tribune.
Attributed

Source: Batman: Hush, Vol. 1

Journal entry (14 October 1922), published in The Journal of Katherine Mansfield (1927); these are the final words of the journal
Context: This all sounds very strenuous and serious. But now that I have wrestled with it, it's no longer so. I feel happy — deep down. May you be happy too. I'm going to Fontainebleau on Monday and I'll be back here Tuesday night or Wednesday morning. All is well.

Entry in her journal (10 October 1922) which she tore out to send to John Middleton Murry, before changing her mind. This later became the last published entry in The Journal of Katherine Mansfield (1927) edited by J. Middleton Murry
Context: Warm, eager, living life — to be rooted in life — to learn, to desire to know, to feel, to think, to act. That is what I want. And nothing less. That is what I must try for. … This all sounds very strenuous and serious. But now that I have wrestled with it, it’s no longer so. I feel happy — deep down. All is well.

Source: Dash & Lily's Book of Dares

First years at School, p. 25
Brother Ray : Ray Charles' Own Story (1978)

Source: The Five People You Meet in Heaven - Meniti Bianglala

Variant: Then it hit me and I just blurted, 'I like people too much or not at all. I've got to go down deep, to fall into people, to really know them.
Source: The Unabridged Journals of Sylvia Plath