If people are going to do something effortful, they want to know that their effort is going towards their goal.
In the app, this can be communicated through Progress monitoring and feedback systems that show how the app is instrumental to goal achievement. It can also be communicated through other UX that shows the user concrete pathways to goal achievement. This is what allows you to Speak to the user with a shared vocabulary
Many “aha moments” can be encapsulated through this principle.