Before I go any further, mine is appalling. Like a lot of people, I sometimes wonder whether I am at the early stages of Alzheimer´s, I get embarrassed because I forget someone’s name or something important they have told me and my speed of recall would automatically disqualify me from any kind of quiz show, should I ever be tempted to participate in one. In language classes, lack of memory is the biggest complaints and sources of embarrassment, irrespective of the intelligence of the student and their original understanding of whatever it is they have now forgotten.
If you see yourself reflected in these comments, then I would like you to know that you are absolutely normal (in this respect at least). Nobody, unless they are some kind of genius, is able to remember language after only hearing it, or repeating it only once. Think back to your childhood, or that of your children and grandchildren. How did we acquire language, if it wasn´t through hearing it repeated constantly? We went through a process, from passive to active, in assimilating language. In other words, we had to hear a word many times before we understood it and then quite a few more times before we felt capable of using it ourselves in a meaningful way. Even then, the first time we tried out a new word we would sometimes use it inappropriately and have to be corrected.
If that is the process of first language acquisition in children who are at the optimum age to learn language, how much more is going to be the case for us learning a foreign language at our great age? There will only ever be very few words, if any, that you will retain the first time you hear them. The most common process is to hear a new word, repeat it and forget it, hear it again, repeat it again, forget it again, hear it a third time and think it sounds vaguely familiar, forget again and so on, and it is the job of people like me to patiently repeat the word as though it were completely new, and without showing any sign of impatience, in the knowledge that the process is simply normal for all of us.
Of course this leads the inevitable nag, which is that most of this repetition has to be self-motivated and done away from a language class. Going over and over what we are taught is one part of the process and the other is to find opportunities to listen to the spoken language as much as possible. There is no excuse if you have a computer. You can watch anything you like on Youtube: songs, cookery demonstrations and tips on stain removal and golf swings, in Spanish, at any moment of the day or night.