What theme is emphasized in this excerpt from "Ode on a Grecian Urn" by John Keats?

Heard melodies are sweet, but those unheard
Are sweeter; therefore, ye soft pipes, play on;
Not to the sensual ear, but, more endear'd,
Pipe to the spirit ditties of no tone:
Fair youth, beneath the trees, thou canst not leave
Thy song, nor ever can those trees be bare;
Bold Lover, never, never canst thou kiss,
Though winning near the goal yet, do not grieve;
She cannot fade, though thou hast not thy bliss,
For ever wilt thou love, and she be fair!

A.
Only things that continually change are true.
B.
Unfulfilled desires and dreams seem sweeter.
C.
Incidents and events depicted in art are true.
D.
Art does not last forever; only memory does.
E.
Incidents and events depicted in art are untrue.

Read this excerpt from i never had it made. "it's all that ought to count," he replied. "but it isn't. maybe one of these days it will be all that counts. that is one of the reasons i've got you here, robinson. if you're a good enough man, we can make this a start in the right direction. but let me tell you, it's going to take an awful lot of courage." he was back to the crossroads question that made me start to get angry minutes earlier. he asked it slowly and with great care. "have you got the guts to play the game no matter what happens? " "i think i can play the game, mr. rickey," i said. the next few minutes were tough. branch rickey had to make absolutely sure that i knew what i would face. beanballs would be thrown at me. i would be called the kind of names which would hurt and infuriate any man. i would be physically attacked. could i take all of this and control my temper, remain steadfastly loyal to our ultimate aim? which is the central idea of this excerpt?