语篇填空，阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空。
Creating good habits can be as tough as breaking bad habits. From my experience, one of the most important factors ____ make forming a new habit hard is that a lot of willpower ____ (require), at least in the beginning, and that alone can prevent many people correctly developing their desired habits.
Now instead of just using willpower and reminding ____ (you) to start the new habit each day, why don't you just link it to an existing one? I have done ____ experience. It started with just 20 pushups (俯卧撑), something easy. So before I showered each day, I would do the pushups. ____ a couple of days, I increased the amount just to make it a bit more challenging.
Gradually, over the course of about 3 months, I'm now doing 100 pushups. And as the habit grew stronger, it got easier to do so ____ (natural). Now I know the habit is pretty much ingrained (根深蒂固), for I feel like something is missing ____ I don't do this before showering. I found it pretty easy ____ (create) this habit and not much willpower was involved.
I think the key, apart from using an ____ (exist) habit, is to start out with something really easy. Once that starts becoming part of your ____ (day) routine, add on to it.
