“3769. One may as much miss the Mark, by aiming too high, as too low.”
Introductio ad prudentiam: Part II (1727), Gnomologia (1732)
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Thomas Fuller (writer) 420
British physician, preacher, and intellectual 1654–1734Related quotes

“Do not aim low, you will miss the mark. Aim high and you will be on a threshold of bliss.”
Source: Light on Life: The Yoga Journey to Wholeness, Inner Peace, and Ultimate Freedom, p. 177

Attributed without citation in Ken Robinson, The Element (2009), p. 260. Widely attributed to Michelangelo since the late 1990s, this adage has not been found before 1980 when it appeared without attribution in E. C. McKenzie, Mac's giant book of quips & quotes.
Disputed
Variant: The greatest danger for most of us is not that our aim is too high and we miss it, but that it is too low and we reach it.

“My fees are not too high. Your wage scale may simply be too low.”
Source: Showboat World (1975), Chapter 12 (p. 132)

“We aimed far and high, but we did not miss the mark.”
Part 4, 1979 - 1984 "Welcome to the 1980's", p. 340
Memoirs (1993)
“I will commit not the terrible crime of aiming too low.”
Source: The Greatest Salesman in the World (1968), Ch. 15 : The Scroll Marked VIII, p. 91.
Context: I will commit not the terrible crime of aiming too low. I will do the work that a failure will not do. I will always let my reach exceed my grasp.

The Spirit of Liberty: Papers and Addresses (1952), p. 9.
Extra-judicial writings