“You can’t keep a good man down” is a popular saying that means a good person will persevere and triumph over adversity. The saying dates to the 1880s.
 
“It’s hard to keep a good man down” was cited in an Indianapolis (IN) newspaper from April 1881, and “Yer can’t keep a good man down” was cited in an Evansville (IN) newspaper from January 1882. “You can’t keep a good man down” was cited in a Missouri newspaper from February 1883.
 
“You can’t keep a good market down” (about the stock market) was cited in the 20th century.
 
   
The Free Dictionary
You can’t keep a good man/woman down. (humorous)
something that you say which means that a person with a strong character will always succeed, even if they have a lot of problems
 
23 April 1881, The People (Indianapolis, IN), “Journalistic Notes,” pg. 6, col. 2:
Misery loves company. The most cheering bit of news we have is that while we laid on our back two weeks getting up the Argus, while we wrestled with pneumonia, our old friend, Enos B. Reed, of Indianapolis, was lying on his back getting up The People, while he struggled with rheumatism. We got out a splendid paper, however, and sold every one, and Reed did the same, which all goes to prove that “it’s hard to keep a good man down.”—Evansville Argus.
     
20 January 1882, Evansville (IN) Daily Courier, pg. 4, col. 5:
“Yer can’t keep a good man down. Like grease, he will swim on top.”
 
Chronicling America
2 December 1882, Greenville (MS) Times, pg. 3, col. 2:
Colonel Isaac A. Newman, formerly of Greenville, Mississippi, more recently of Eureka Springs, Arkansas, has now taken charge of a hotel at Fort Smith, Arkansas, and is booming. Can’t keep a good man down.
 
Chronicling America
22 February 1883, Mexico (MO) Weekly Ledger, pg. 3, col. 5:
Rev. Silas Smith has both lots in South Mexico and will at once proceed to erect a church building. Smith says you can’t keep a good man down.
 
Google Books
March 1885, Frank Leslie’s Sunday Magazine (T. De Witt Talmage, D.D., Editor), pg. 257, col. 1:
THE HOME-PULPIT.
SERMON, BY THE REV. DR. T. De WITT TALMAGE, PREACHED IN THE BROOKLYN TABERNACLE.
FROM DUNGEON TO PALACE.
(...)
You cannot keep a good man down. God has decreed for him a certain point of elevation. He will bring him to that though it cost Him a thousand worlds.
 
OCLC WorldCat record
You can’t keep a good man down
Publisher: Orange, N.J. : National Phonograph Company, [1901]
Edition/Format:   Music : Wax cylinder : Songs   Archival Material : English
 
OCLC WorldCat record
You can’t keep a good man down
Author: Dan W Quinn
Publisher: Camden, N.J. : Victor Talking Machine Co., [1906]
Edition/Format:   Music : Reel-to-reel tape : English
 
OCLC WorldCat record
You can’t keep a good man down
Author: Perry Bradford; Albert A Smith; Sophie Tucker
Publisher: New York (1547 Broadway, New York City) : Perry Bradford, ©1920.
Edition/Format:   Musical score : English