How things become easier when we do things continuously / repeatedly?

What are habits, and why do they stick? Lord Buddha said that we even bring habits into next lives. Why does that happen? How come it is powerful enough to continue from life to life? There are some variations of habits. Some needs mental effort (like studying, or meditating etc.), some needs physical effort (exercising etc.), and some doesn't need any effort, meaning that every day actions (eating, playing etc.). (By effort i mean the energy needed to do something, and habits requires less actual effort to do something). I have the general idea about how habits works. We may be able to find shortcuts, and get new ideas when we do things repeatedly. But, it is hard to understand the way our habits vary. Can anyone give me a clear / deep explanation about habits? Or are habits conditioned by impermanence, cause and effect or karma that I should accept as the nature of existence/the world? If it is, please post the name of respective sutta where Lord Buddha talked about habits, so I will be able to believe it without doubts. Kind regards.