Because that's the thing. I am so intimately familiar with deadlines, after such a long relationship, that I know all too well, I will get the thing done. But that also means, I have lost the ability to get it done early. I no longer finish far ahead, because I no longer feel I need to make sure I'll finish. So I must go through the torture of feeling that I won't get it done, even though rationally, consciously I know I will, which is why I'm acting like this.
Some terrible force -- the same force that makes me blog? -- drives me to throw away all the extra time. I must create panic, apparently, so that my current little writing project becomes like a silent movie where the heroine is tied to the railroad tracks and the hero must arrive at the very last second. Isn't that so much more exciting?
So I'm blogging my time away, writing this -- easily! -- when I have 1200 words I need to nail down to meet a deadline. I've casually tossed more than 1200 words onto this blog today, even as a feeling of dread has been closing its grip on me. The deadline!
Yet still, I take the time to follow the urge to find something online about the general abstract idea of the deadline. But the train tracks! The heroine! No, no... I know what I'm doing... Look, isn't this interesting?
The sense of deadline meaning a time limit was originally newspaper jargon and first appears in 1920. It is an Americanism. It may derive from printing jargon referring to a guide that is placed on the press to keep the type in place. This sense appears a few years earlier.
The sense meaning a line around a prison where the prisoner's will be shot if they cross it, comes from the 1860s and prison camps during the American Civil War. The angling sense dates to 1860 or perhaps a bit earlier. These may or may not have had an influence on the newspaper term.
Ah, now! Get to work. You're out of your mind!