“Knowledge becomes useless and wasted if it is not acted upon or put into practice.”
Related quotes

“Knowledge is of no value unless you put it into practice.”

“Great thoughts reduced to practice become great acts.”
"On the Knowledge of Character"
Table Talk: Essays On Men And Manners http://www.blupete.com/Literature/Essays/TableHazIV.htm (1821-1822)

“When knowledge is put into practice that’s when wisdom is born within a person.”

“Faith and knowledge lean largely upon each other in the practice of medicine.”
Book II, p. 408.
Collected Works

Biharul Anwar, Volume 1, Page 222
Shi'ite Hadith

“Contingency time is useless wasted time, right until you need it.”
Source: The Laundry Files, The Labyrinth Index (2018), Chapter 8, “A Game of Vampires” (p. 236)