I have been having the same issue becuz it's so dang cold here right now; in the summer, I love to walk and do, but in the winter I find it hard to face that cold wind, and -20C to -30C temps. I agree with setting aside a special time to go walk; I do that too (that's my newest strategy). I also do the store shopping and walking method for some of the days like RN suggested; I purposely walk around the entire outside of our grocery store which covers from veggies to frozen foods and avoid the junk aisles completely.
Many doctors are suggesting 60 minutes of total exercise for 5 days for weightloss, but I started out at 5-10 minutes just walking around our yard, then parking lot, and now up and down our very long laneway to the back of our lot. Once you are out there, the time just seems to fly by. I also do other exercises indoors at 5-10 minute increments throughout the day.
I agree that it is a choice we have to make. Make a commitment or deal with yourself to do this. I know if I wait for motivation, I won't ever do it becuz I can find too many excuses. Tell yourself you have to do it for your health's sake, and that's it ...
I agree about changing where you go walking might help too; go somewhere different each day. I prefer to go to parks, lakes, the country, to stores, malls, and the like; it makes it go so much faster. Ever noticed that when you are walking around a mall or store, you don't even think about the fact that you are actually exercising, but you are!