Now, just because you recognize what your ear is trying to tell you doesn’t mean you have to follow that advice. Play your first chord, and then listen for your metal ear’s advice. When you know what it wants you to play, you are then left with a choice: you can follow it or reject it.
If you reject the chord given to you by your mental ear unintentionally too often, you will likely dull your capacity to find the chord that your mind suggests. This will make it difficult to write by heart, because rather than writing music by heart, you will be left to take guesses and choose chords either randomly or by knowledge alone, neither of which are very effective.
The best way to prevent this is to pay close attention. If you play a chord and it doesn’t match the note or chord suggested by your mental ear, stop and try another chord. If you find that you’ve already forgotten what that chord was supposed to sound like, start over with the first chord again. By paying careful attention to the notes or chord that your mental ear suggests, you will find that your metal ear has a great memory, as well as good taste in music!
If you are given a note by your mental ear, you can choose to reject it. It’s okay to use a different chord than what your mental ear suggests, as long as you are doing it knowingly and intentionally. Rejecting a chord intentionally will, to some extent, re-configure your mental ear to listen for that different chord or note. In other words, any time you begin writing a piece of music for the first time, as you approach the time to play a new chord, your mind will tell you what chord to play. If you choose those chords as your mind tells you, you will be able to write your piece quite easily. If you choose a different chord, you may be able to find a chord that you like even better. The bottom line is, you must have your mind, heart, and fingers trained to be able to play a chord that you hear (audibly or mentally) so that you can choose whether or not to use those chords or notes.
The great thing about choosing a different chord than your mental ear suggests is that in finding new chord progressions, you create for yourself a whole new library of possibilities for your mental ear to draw from. The more you try new things and learn to work with new ideas, the more you will have to build with. This becomes a remarkable adventure. You will find that most any two chords can work together if you take time to discover when and where and how to play them. With your mental ear and your creativity as your guide, there are very few limitations to your potential.