When I first started trying to lose weight, I was too out of shape to even make it through week 1 of the C25K, so I started walking instead. I walked several miles a day for many months before trying the C25K again. When I finally felt comfortable trying to run again, I hated to give up my walking, so I just added the C25K program to my daily workout. Most days I was walking 3 miles on my lunch at work, 2-3 miles with my dog after work, then 3 days a week also doing the C25K program in the evening. Or I would do the C25K program, get done, run back to my apartment to get my dog, then do her 2-3 mile walk as my cool down. I now do all my regular walking in addition to running 3 miles every other day and feel great when I get done with everything. If your body seems okay with it, then I would go for it. Just pay attention to how your body responds and scale back a bit if you start to have problems.
It's not that some people have willpower and some don't. It's that some people are ready to change and others are not.
My progress pictures