Maybe you don't care enough about the other person, the subject, your relationship to that person. Maybe your time is limited, maybe you think you've heard it all before. Maybe you're so self-absorbed, you can't let anyone else through. These steps are land mines if you aren't aware of their value to the listening process. Yes, you have to focus, avoid interrupting, avoid your distractions.
Understanding involves learning what the other person means.
Understanding involves learning, deciphering meaning, and interpreting with fidelity to the intended message. Remembering or, rather, reconstructing messages is a third step in the listening process. Recalling or retaining messages by reconstructing them into something that makes sense to you is a skill that can be practiced and improved, of course. A fourth step, evaluating, is hard not to do. It's easy for us to judge and criticize.