It is habitual for a person to take the other person for granted, especially when those two people understand and know each other personally on a different level. For instance, a couple in a romantic relationship may sometimes ignore each other purposely and may hurt each other unintentionally, but in the end, that couple can still create the same old lovey-dovey environment easily without giving a chance to any gaps that separate them from each other and that's called Love.
But sometimes, under the name of love, a person may take an advantage of one's partner by assuming that everything would be the same regardless of how one behaves. This silly perception is very common in any romantic relationship, and this arises after spending a good number of years with a romantic bond. Unfortunately, this is the very reason why many couples are falling apart from each other even though they maintain an inseparable intimate rapport in their relationship.
It all starts with assuming that you know your partner very well than anyone else in the world. Needless to say, any person in a relationship thinks that he knows his partner better but no one can perceive, predict, and completely comprehend what's running in the other person's mind in every single moment of life. When it comes to individualities, even romantic partners aren't exceptions. So, stop thinking that you know your partner and consider that your partner would understand your situation by default, especially when your situation is not at all worth supporting or hearing out.
Priorities do matter. Your partner always wants you to prioritize him/her/them at any moment of your relationship. A true partner understands when you fail at prioritizing due to ethical commitments, professional issues, and communication disturbances, but when you ignore your partner even though you have every possible way to reach your partner, then it specifies that your partner is someone whom you no more consider seriously.
You can't commit a grave mistake and expect others to entertain and accept you the way you are. Similarly, you can't ignore your partner in her face and expect her to behave normally with you. Now you may wonder, why would someone do that to one's partner out of nowhere. Regrettably, many of us do this to our partners in the assumption of being considered normal regardless of how stupid we behave with our loved ones.