“It's only terrible to have nothing to wait for.”

Le pénible fardeau de n'avoir rien à faire.
Epistle 11

Source: Mr. Fox

Variant: It is nothing to die. It is frightful not to live.
Source: Les Misérables

De Augmentis Scientiarum, Book II, Fortitudo (1623)

Charles Frederick Webber interviewed at a field hospital following the Battle of Gettysburg. He was holding his hand, from which the ends of four fingers had been shot off. He was smoking his pipe with with no sense of urgency and was allowing more wounded soldiers to go ahead of him. He died on July 19, 1863, 13 days after the wound, from the subsequent infection.
Quote
Source: [The Wounded, New York Herald, https://en.wikisource.org/wiki/New_York_Herald/1863/The_Wounded, July 6 1863]

Context: (Answering "What made you step up to making your own record?") I felt like I may not get opportunities to do this ever again, so it’s about time—it’s a terrible thing, I think, in life to wait until you’re ready. I have this feeling now that actually no one is ever ready to do anything. There’s almost no such thing as ready. There’s only now. And you may as well do it now. I mean, I say that confidently as if I’m about to go bungee jumping or something—I’m not. I’m not a crazed risk taker. But I do think that, generally speaking, now is as good a time as any.

Variant: If I ever fall in love again, I will not wait to love as best as I can. We thought we were young and that there would be time to love well sometime in the future. This is a terrible way to think. It is no way to live, to wait to love.
Source: What is the What: The Autobiography of Valentino Achak Deng (2006), Ch. 21, pp. 317-318
Source: What Is the What
Context: I cannot count the times I have cursed our lack of urgency. If I ever love again, I will not wait to love as best as I can. We thought we were young and that there would be time to love well sometime in the future. This is a terrible way to think. It is no way to live, to wait to love.

Source: The Curious Incident of the Dog in the Night-Time

Source: What Matters Most is How Well You Walk Through the Fire