There is a strong inclination that most of us have to seek parity in our connections with others. When we're interested in them, we would like them to be interested back. When we take the time to call, it'd be nice if they pick up the phone and show the same level of initiative. When we love someone, we want them to love us back with similar intensity. When we have a sexual connection with someone, we want them to desire that just as deeply. We'd have the same level of interest in getting together, at the same frequency.
In an ideal world, all those things would happen. They'd even happen naturally, without talking about it. Guess what? We don't live in an ideal world. There are going to be things that lack parity in our relationships, where that level difference can be a deal-breaker. It can also be something that pushes one to grow in a direction they would not have chosen independently.
Maybe you aren't comfortable asking for what you want. Inexplicably, you find yourself strongly drawn to a person who seems oblivious to what you desire from them. This could be just the nudge you've needed to be more assertive, to learn to take a no, or how to earn a yes from someone you feel connected to. It could also demonstrate the need to take a look at partner selection skills again, to help identify connections that would be more attuned to your needs, less self-centered.
Perhaps you find yourself in a relationship where the sexual component has fizzled on one side or the other. This could be a great opportunity to explore and reinvent the connection. To stop going on auto-pilot, or to look at having those needs met with a different partner if there is an unwillingness/incapacity with the first partner.
What if you are doing all the chasing with someone? You send the emails, plan the dates, make yourself available, and the best response in return is to elicit participation on a sporadic basis, if it's convenient to the other person. Do you enjoy the hunt that deeply? Is a one-sided connection going to be satisfactory as time goes by? Do you crave being crushed under foot as they walk all over you? Now is the time to stand up tall and walk away, or to reduce the amount of energy you are pouring into a given connection, and see if that starts to equalize.
There is no perfect formula, and every relationship will have some level of disparity in some aspect of the connection. Those uneven spots can be where you find the most growth, and ultimately, the deepest understanding of your own needs and wants.