In order to make a habit, the result of that habit has to be rewarding. It's very unlikely you will create a habit that costs you or harms you.
It's hard to say, coming from a completely evidence-based standpoint, that living by faith always guarantees a reward. After all, that's what faith is, according to Hebrews 11:1: "Now faith is the substance of things hoped for, the evidence of things not seen". And even if living in faith always guaranteed a reward, it's impossible to know what that reward will look like or when it will be received. So living by faith would be by definition harder to make a habit.
For example, an individual wants to create a daily habit of eating a balanced diet and daily exercise. His reward of establishing this habit would then be a more appealing physique through weight loss and muscle gain. He might also feel better due to balanced nutrition meeting his energy requirements and healthy use of his muscles and joints to increase his ability to be active. So the result, a more appealing physique and increase in energy levels, will have a greater payoff than the cost of the investment, sacrificing Vanilla ice cream every night and sweating for 20min three times a week.
I believe this same concept can be applied to persons of Christian faith. I want to talk about how a person keeps a "habit" of believing in God (i.e. faith), even though there seems to be no consistent reward. And although you may think that I'm vouching for the person of faith due to my background, I'm actually writing this because it's sometimes difficult for me to conceptualize how the benefits of believing in an unseeable God outweigh the costs.
It seems to be that as I grow stronger in faith, I also become better at identifying what right and wrong is, what goodness and evil is. The more I understand who God is, the more I understand just how sinful and imperfect I am and will always be. I believe this is because when I fall away from faith, I'm numbed to the difference between right and wrong. I don't have to think about what righteous and what's not, because without Jesus, it doesn't matter either way.
There could also be a point, though, when I hit "rock bottom" and feel purposeless because I feel I'm not contributing any goodness to the world around me. At that point, I'm more motivated to desire a stronger relationship with the Lord because I want to contribute goodness to others instead of evil.
I'm sure many fellow believers can relate to this. And just from experience and my own observation, I believe that's why there are so many of us that feel as though we're "lukewarm" Christians. We're in an endless loop of finding the Lord, becoming stronger in faith, but then eventually feeling discouraged because we feel we can't live up to the high standards God holds for us or the standards our church community holds for us. As a result, we draw away from faith because we start to notice our unholiness the closer we get to the Lord.
So what is different in those that have a somewhat unsteady relationship with God, and those who make a habit of living their life in strong faith? Let's define this habit as praying daily, reading the Bible multiple times a week, and actively being part of a church community. Considering that faith doesn't seem to have an expected reward (at least during this time here on earth), how does someone of strong faith continue to read, pray, and worship? What's different between someone who has a strong relationship with God compared to someone who has a hard time staying close with God? Because both of them theoretically will become discouraged at one time or another due to the guilt that is often accompanied by sin.
If you asked any Christian this, they will probably say that's it's a feeling. It's the feeling of God's grace, forgiveness, love, and mercy that gives a person who maintains a strong relationship with God a desire to read the Bible, pray, and keep community with other believers, despite not knowing when or what the payoff will be. They know that even though they will sin, God won't keep them accountable for that sin as long as they repent.
They might also say that the perception of religion might be different between the two types of individuals. An individual who maintains a strong relationship with God might see Him as a father figure, while the other person might see Him as more of a judge. Thus, there is more of a genuine love for God in the person of strong faith, while there is more of a fear of God in the person who has a more difficult time keeping faith (not the good type of fear-- the bad one).
So how does this relate back to the idea of creating a habit? After discussing the differences in perception of the two individuals, one would say that the reason the person who keeps their habit of reading weekly, praying daily, and staying apart of a church community is the reward of feeling loved, doing good, and pleasing a father-like figure of Christ (realize, that being sin-free is NOT one of these rewards), just like the reward of the dieting, exercising individual was an appealing physique. On the contrary, the other individual views their reward as being right with God, or free from sin. This individual may feel as though he/she has to work for the reward of faultless, sin-free character. This is something impossible to earn, since we are and always will be unrighteous by nature. So because he/she sees deeds as the way to attain true righteousness in the Lord's eyes, this individual will never reap the benefits of faith.
I think that there can be another individual in this picture. Let's say you aren't really in need of a reward. Ex. you could start eating healthy and exercising to attain a more appealing physique, but you're satisfied with your current body shape and have no desire to change your lifestyle. So you are less likely to strive to make a habit of dieting and exercise if believe you already reap those rewards. In the same way, I believe there are some individuals who don't see a need for faith, because they are already benefiting from their current lifestyle. Although their peers claim that faith leads to internal happiness and joy despite the challenges and battles of life on earth, this individual already believes he has that without having faith.
Although this may seem like an abrupt ending, I'm purely just laying down my thoughts on this idea. I came about these thoughts after reading Romans 7, where Paul explains how God's law actually has the power to condemn us as humans (if you're confused, just read the chapter for context). I'm trying to find the balance between all of these perceptions and mindsets of faith. It's often difficult because I want to analyze the Bible with a logical, backed-up-by-science mentality, but I also know that the Bible, or heck the idea of God himself wasn't meant to be completely understood through a human mind. So there will always be parts that I can't explain, which in reality is frustrating. Furthermore, I've always had a sort of competitive personality, and when I don't see progress in something I'm passionate about, I'm discouraged. So when I feel as though I'm "lukewarm" in my faith, I put in extra effort to try to mimic the mind of Christ through love, humility, and forgiveness. But like Paul, with that comes more guilt when I mess up. Now this isn't something that keeps me up at night. But I think in the end, this pondering will strengthen my faith. So I just have to tell myself to keep working at the habit, even if I don't know when the benefits will come or what they will be.