Darwin, circa 1859 or 1860. (Wiki Commons.)
“But I am very poorly today & very stupid & hate everybody & everything. One lives only to make blunders.”
— Charles Darwin, letter to Charles Lyell, Oct 1, 1861
Everyone has their bad days.
I Am Very Poorly Today
Patrick F. Clarkin, Ph.D. 
That’s every day for a would be perfectionist like Darwin, who realised with frustration that however long he spent gathering and interpreting data, he would never have enough for a 100% scientific theory. Perhaps the surprising thing is that he never really allowed that scientific theories are never watertight and will always be revised: but then he was up against some powerful opposition in the creationists.
I think that’s right. He was a perfectionist, spending 20 years putting his case together. He was also afraid of the repercussions and what people thought of him.