In DBT you are expected to keep a diary card.  This is a card on which you track the intensity of your emotions, whether you have engaged in any problematic behaviors and whether you used DBT skills to help get through the week.

Diary cards track a lot of information. There are 20 skills alone. You record whether you used them every day.  Each skill has multiple sub-parts.  As part of my training I kept a diary card and found it difficult to complete.  When I listened to music was I self-soothing, distracting, being one-mindful?  Did it matter and was it helping?

The reason you complete a diary card in DBT is to elicit information about targeted behaviors that have occurred during the week.  If behaviors have occurred, they are discussed in therapy.  If patterns emerge, they are discussed in therapy

How does the diary card work?

There is evidence that mood can have a powerful effect on memory and how information is organized, retrieved and processed.  Up-and-down mood and emotions can cause you to remember only the negative or the positive aspects of a situation.  It can interfere with your ability to accurately assess a situation.  Changing your behavior requires accurate information.  Reliance on unaided memory makes it more difficult to obtain accurate information.  Diary cards provide a record of frequency and intensity of problem behaviors.  They are signals of problems that need to be assessed.

How does a therapist know about targeted behaviors that occur between sessions?

Ask.  Asking whether a problem has occurred is simple when it’s occurring often.  But, as you gain control over your behavior, and are working on other issues, it can be easy to let it go.  Life threatening behaviors are always addressed first in individual therapy.  But, if your therapist doesn’t know that they occurred it can’t be assessed.  Diary cards ensure that information is communicated.