People are not "fixer-uppers." You will never be able to alter, control, modify, or otherwise manipulate another person's mode of operating in the world. The best you can do is to set your own boundaries, and decide whether you can tolerate a person the way they are.
Here are four things I've learned the hard way:
1. You can't make someone respond to you: Still waiting for that email, text, or phone call? Stop waiting and think about something else. People respond to you when they're good and ready, and not a minute before. Oh, and "good and ready" might mean "never."
2. You can't change someone's level of sensitivity: People have varying levels of sensitivity. There are some people who will be offended by objectively (or perhaps subjectively) benign interactions. You can't spend your life walking around on egg shells trying not to offend hyper-sensitive people, because a hyper-sensitive person will look for--and find--a reason to be offended at every turn. Likewise, if you yourself are sensitive, it's not realistic to expect others to cater to your sensitivity. I've been in this latter category more times than I care to remember.
3. You can't change someone's habits: Anyone who has ever battled with addiciton or been close to an addict knows this one well. If someone is bound and determined to kill themselves slowly with drugs, alcohol, unhealthy eating, or similar habits, that's their decision. You can decide you won't enable it, but you can't make it stop and you can't make them change.
4. You're not exempt from someone's patterns: Ever notice how certain people have drama that seems to follow them wherever they go? Like they just can't seem to maintain relationships devoid of conflict and drama? They'll tell you a story of their latest conflict, and conflicts seem to arise all the time. Never assume you won't be the center of the next conflict. In other words, don't kid yourself into believing that you're exempt from the pattern.
Nothing drives a person crazier than intermittent reinforcement. They've done studies on this, showing that both people and animals go nuts when they don't know what's coming next or what to expect in a given situation. I've learned to do myself a favor and carefully observe the people in my life. It helps me make conscious decisions about whether I'm going to tolerate whatever their limitations might be, and it sure helps me stay sane. At least some of the time.