I hate that word. This world is so full of failure. You can't hide from it. You can't not fail at something, sometime, somewhere. Wow, great pep talk, huh?
The good news about failure is that it's not the end of the world. It's a part of life, so you just need to embrace it. Embrace it and move on! There should be no wallowing in your failures. Wallowing is just like worrying - it only creates stress, not solutions.
One thing to help ebb failure is to be sure your expectations are real. I didn't get my DVD workout done last night, but it wasn't realistic for yesterday that I would play volleyball, run 3 miles, and do a DVD workout. 2/3 is really good! It was still an hour workout (hour plus).
You've come face to face with failure. If you haven't, pop out a couple of kids and it'll happen quickly. Trust me. I toe the line of "failure" constantly as a mother, but I don't wallow in it (except for a few tears). I pick myself back up, talk to the Lord about it, and go on with life.
God gave me my children to mother, so I am the person made for the job. God gave me my body, so I am the person to improve it and utilize it! There was no oversight on His end; that just doesn't happen. You were made to be who you are at this exact moment for a purpose greater than yourself.
So maybe you ate too many chips, one too many slices of cake/pie/whatever. Maybe you missed your workout yesterday (and the day before, and the day before). Maybe you haven't worked out in years. It doesn't mean that your failure defines you! It will if you let it, but it doesn't have to.
I put on so many pounds in my pregnancies (and, to be honest, in college beforehand). I felt like a failure in the health department. But I wasn't. I had failed. One failure doesn't make you a failure. Just like one mess up as a mom (yelling at your kid, being impatient) doesn't make you a bad mom! It just means that we're all fallible. There was this Fall at the beginning of the world that causes us to suck sometimes. It's not an excuse. My being tired doesn't give me an excuse or pass to be grumpy and impatient with my kids. My being lazy doesn't give me an excuse to pass up an opportunity to workout! No, it's an explanation, not an excuse!
So quit excusing yourself from life - from being healthy, from being a good mom/daughter/sister/wife/friend - just because you have failed once, even twice, even 70x7. Because you can always dust your pants off, put on your big girl pants, and move on with life. We're all trying our best out here, that's all anyone can ask (enough with the "give 110%" talks people. It's just not possible!).
Do your best today. Start. Start over. Seek forgiveness. Feel mercy. Move on.