決して諦めない is a plain sentence of resolve. 決して, with a negative, means never. 諦めない is not giving up. 諦める is to stop because you see no hope, and its first character, 諦, is to see a thing clearly and let it go. So the line holds on even when the end looks plain to see. It reads as a resolution rather than a shout. Whether it is for your own training or for someone in a long fight is yours.
Never Give Up is the refrain of Martin Farquhar Tupper's ballad Never give up!, in print by 1845; Churchill's words at Harrow in 1941 were never give in. The Japanese 決して諦めない is in print by 1918, of the French army.
We want you to be as happy with the meaning as you are with Master Takase's art. To learn more, visit Philology of 決して諦めない.