Many times a day I realize how much my own outer and inner life is built upon the labors of my fellow men, both living and dead, and how earnestly I must exert myself in order to give in return as much as I have received. My peace of mind is often troubled by the depressing sense that I have borrowed too heavily from the work of other men.

Albert Einstein (1879-1955) German-American physicist

“What I Believe,” Forum and Century (Oct 1930)
    (Source)

Einstein crafted and recrafted his credo multiple times in this period, and specifics are often muddled by differing translations and by his reuse of certain phrases in later writing. The Forum and Century entry appears to be the earliest. Some important variants:

A hundred times every day I remind myself that my inner and outer life are based on the labors of other men, living and dead, and that I must exert myself in order to give in the same measure as I have received and am still receiving. I am strongly drawn to a frugal life and am often oppressively aware that I am engrossing an undue amount of the labor of my fellow-men.

— "The World As I See It [Mein Weltbild]" [tr. Bargmann (1954)]

A hundred times every day I remind myself that my inner and outer life depend on the labours of other men, living and dead, and that I must exert myself in order to give in the same measure as I have received and am still receiving. I am strongly drawn to the simple life and am often oppressed by the feeling that I am engrossing an unnecessary amount of the labor of my fellowmen.

— "The World As I See It [Mein Weltbild]" [tr. Harris (1934)]

I am often troubled by the thought that my life is based to such a large extent on the work of my fellow human beings, and I am aware of my great indebtedness to them.

[Oft bedrückt mich der Gedanke, in welchem Maße mein Leben auf der Arbeit meiner Mitmenschen aufgebaut ist, und ich weiß, wie viel ich Ihnen schulde.]

— Reduced variant in "My Credo [Mein Glaubensbekenntnis]" (Aug 1932)