Habits are like that. We develop particular actions and attitudes over time and they are very difficult to change. The way we react to certain things, the way we think, the choices we make, these are all habits. Over time we conform to those habits simply because we have doing them for so long.
God tells us not to conform to the patterns of the world but to renew our minds. (Romans 12:2). Easier said than done. Paul discusses the difficulty of changing our ways in Romans 7:15. "For what I am doing, I do not understand; for I am not practicing what I would like to do, but I am doing the very thing I hate." Paul understood the laws of human nature and habits. But he also knew the path to that change - renewal of the mind.
What we think determines our actions. If we can change our minds, we will change our actions. The only way to renew our minds so that we think and act in a godly way is to spend time reading and meditating on God's word and then practice what we read. The more we fill our minds with God's love and truth, and the more we actually do what it says, the more natural it will become.
It may take me a while to remember to reach to the middle for the toothpaste, but in the meantime, I am still brushing my teeth. I won't give up just because I forget at first. I just hope it doesn't take me seven years to remember!