Putting something off is self-reinforcing. You think you're just going to put the thing off once. But doing that, it gets a little more tempting to put it off for next time. Because you've given yourself evidence that it sucks to do the thing. You've already put it off once, so it now feels slightly shittier, so next time you will want slightly more strongly to put it off again.
This is frustrating.
(No, I'm not putting anything off by writing this post. Why do you ask?)