“In the midst of all this great variety of subjects, an individual cannot attain to perfection in each, because it is scarcely in his power to take in and comprehend the general theories of them.”

Source: De architectura (The Ten Books On Architecture) (~ 15BC), Book I, Chapter I, Sec. 15

Actually from one of John Dewey's lectures, reprinted in his Reconstruction in Philosophy (2004), p. 96.
Misattributed

On Alan Coren, p. 166
Memoirs, North Face of Soho (2006)

Grundrisse (1857-1858)
Source: Notebook I, The Chapter on Money, p. 76.

Boulding (1958) "Evidences for an Administrative Science: A review of the Administrative Science Quarterly, volumes 1 and 2". In Administrative Science Quarterly. vol. 3, no. 1, pp. 14
1950s

Notes from Devotional Authors of the Middle Ages (1873-1874)
Context: These old Mystics whom we call superstitious were far before us in their ideas of God and of prayer (that is of our communion with God). "Prayer," says a mystic of the 16th century, "is to ask not what we wish of God, but what God wishes of us." "Master who hast made and formed the vessel of the body of Thy creature, and hast put within so great a treasure, the Soul, which bears the image of Thee": so begins a dying prayer of the 14th century. In it and in the other prayers of the Mystics there is scarcely a petition. There is never a word of the theory that God's dealings with us are to show His "power"; still less of the theory that "of His own good pleasure" He has " predestined" any souls to eternal damnation. There is little mention of heaven for self; of desire of happiness for self, none. It is singular how little mention there is either of "intercession " or of " Atonement by Another's merits." True it is that we can only create a heaven for ourselves and others "by the merits of Another," since it is only by working in accordance with God's Laws that we can do anything. But there is nothing at all in these prayers as if God's anger had to be bought off, as if He had to be bribed into giving us heaven by sufferings merely "to satisfy God's justice." In the dying prayers, there is nothing of the "egotism of death." It is the reformation of God's church—that is, God's children, for whom the self would give itself, that occupies the dying thoughts. There is not often a desire to be released from trouble and suffering. On the contrary, there is often a desire to suffer the greatest suffering, and to offer the greatest offering, with even greater pain, if so any work can be done. And still, this, and all, is ascribed to God's goodness. The offering is not to buy anything by suffering, but — If only the suppliant can do anything for God's children!
These suppliants did not live to see the " reformation" of God's children. No more will any who now offer these prayers. But at least we can all work towards such practical " reformation." The way to live with God is to live with Ideas — not merely to think about ideals, but to do and suffer for them. Those who have to work on men and women must above all things have their Spiritual Ideal, their purpose, ever present. The "mystical " state is the essence of common sense.

Source: Self-Reliance

Les artistes qui cherchent la perfection en tout sont ceux qui ne peuvent l'atteindre en aucune partie.
Quote, 4 March 1858, from Journal de Eugène Delacroix, book 3
1831 - 1863, Delacroix' 'Journal' (1847 – 1863)