If your goal becomes somewhat unrealistic, is it better to scrap it and set a smaller one, or to keep reaching for it?

I’ve set a mileage-based fitness goal for myself this year, and because of a few days that turned into a week into a few weeks into almost a month (you know how it is), I’m a little behind on it. I’ve realized that it’s probably just not going to happen unless I push so hard that there’s a good chance of injuring my body, which I obviously want to avoid. Achieving it is still a possibility, it’s just not likely.

Is it better to just do the best I can, still try for it, but be realistic about it, and try again next year if I don’t make it, or is it better to re-evaluate, and set a smaller, more realistic goal for this year, in light of the situation?

What are your thoughts?