Do not permit what you cannot do to interfere with what you can do.
John Wooden (1910-2010) American basketball player and coach
Coach Wooden One-on-One, “Day 25” (2003) [with Jay Carty]
(Source)
Variant: "Do not let what you cannot do interfere with what you can do."
Quotations about:
block
Note not all quotations have been tagged, so Search may find additional quotes on this topic.