“The Only Easy Day Was Yesterday” is a motto associated with Navy SEAL training at Coronado. Its meaning is straightforward: yesterday’s effort is behind you, and today brings another challenge to meet.
What does “The Only Easy Day Was Yesterday” mean?
One way to read the line is that yesterday's difficulty is finished, while today's still asks something of you. Completing a hard task does not make the next one automatic.
Where does the phrase come from?
The Navy’s All Hands magazine documented the phrase in December 1987. In “Behind enemy lines,” it identifies the saying as the motto of the SEAL training center at Coronado, where Basic Underwater Demolition/SEAL (BUD/S) students trained.
That provides a dated record of its use in SEAL training. The article does not identify who coined the phrase or establish its first-ever use, so December 1987 should not be treated as its invention date.
The design
The shirt pairs “THE ONLY EASY DAY WAS YESTERDAY” with mountains, a circular sky motif and “EST. 1962.” A flag appears on the right sleeve.
Source
“Behind enemy lines,” All Hands, p. 32, hosted by Naval Special Warfare Command, records the phrase as the motto of the SEAL training center at Coronado. The record does not say who first said it.