Trifles make perfection, and perfection is no trifle.
Michelangelo (1475-1564) Italian artist, architect, poet [Michelangelo di Lodovico Buonarroti Simoni]
(Attributed)
The first appearance of this attribution is in C. C. Colton, Lacon: Or, Many Things in Few Words, Vol. 1, § 168 (1820), with no citation as to where he found it (if he did not make it up himself).
Quotations by:
Michelangelo
If people knew how hard I work to get my mastery, it wouldn’t seem too wonderful after all.
Michelangelo (1475-1564) Italian artist, architect, poet [Michelangelo di Lodovico Buonarroti Simoni]
(Attributed)
The earliest attributions only go back to the Twentieth Century (e.g., 1929) in non-academic contexts. No original source is known.
A related attribution, regarding the Sistine Chapel -- "If you knew how much work went into it, you would not call it genius." -- only can be found in the Twenty-First century (e.g., August 2001).
The true work of art is but a shadow of the divine perfection.
Michelangelo (1475-1564) Italian artist, architect, poet [Michelangelo di Lodovico Buonarroti Simoni]
(Attributed)
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.
Michelangelo (1475-1564) Italian artist, architect, poet [Michelangelo di Lodovico Buonarroti Simoni]
(Attributed)
Widely attributed to Michelangelo as of the late Twentieth Century, but without citation.
I am still learning.
[Ancora imparo.]
Michelangelo (1475-1564) Italian artist, architect, poet [Michelangelo di Lodovico Buonarroti Simoni]
(Attributed)
Also rendered Anchora imparo. This is often described as a daily mantra of Michelangelo's. This association can be traced to Richard Duppa, The Lives and Works of Michael Angelo and Raphael (1806) [tr. Hazlitt]. Duppa misattributed to Michelangelo a drawing by Domenico Giuntalodi, which included the saying. The phrase itself was popular during the 16th Century.
While there's no indication that Michelangelo did not say this, or agree with the sentiment, it does not seem to have been solidly cited to him, or shown to be a personal motto, let alone being original to him.
More discussion: Michelangelo - Wikiquote.