I can't think of a solitary day walk I have cut short, not ever, probably because I have been able to wait for the right conditions or conversely I have tailored my plans to the conditions.
When it comes to my multiple-day walks, however, I have probably cut more of them short than I have completed, nearly always because of gale, fog or wetness, once because I unexpectedly became ill.
I've recently failed for the second time to walk all of one particular planned circuit, both times because of the weaather, although one was compounded by some equipment failures. On the latest one I ended up doing almost exactly the same shortened route as before, which left me feeling partly sad and partly angry at the conditions. But they were still prime time spent doing what I like doing out in the wilds, and they were still great experiences.