I'm not sure if stubborn is the right word for either one of them.
Habits are freaking HARD to change. Even simple ones that you might think are insignificant. Many times we know what we're doing wrong and WANT to change it but actually doing the legwork can shake up our life quite a bit.
When I started this journey I cut out sugar/artificial sugar cold turkey. I didn't make any other changes at that time (I was exercising already then, though), which was really a good thing because that took A LOT of work. I had to get out of the habit of buying chocolate every time I went to the grocery store. I had to learn to drink coffee black or with just milk. I had get used to having fruit after dinner, not something with sugar. I really was retraining my taste buds and learning new ways to cook. Add to that that many items that you don't necessarily think of have sugar (some types of chips, bread etc).
Before it wasn't that I was necessarily extremely stubborn but sugar was so ingrained in my life that making that change was difficult. I was able to do it but it took major work.
I'd say anytime you shake up your routine it's going to be difficult. It's not really a matter of being stubborn or not but more dealing with changes in general.