Starting
Picture the obstacle too
Imagining the goal and then the thing most likely to stop you works better than imagining the goal alone.
This method is called mental contrasting, and its practical form is known as WOOP: Wish, Outcome, Obstacle, Plan. You picture what you want, then the most likely thing in the way, then plan for that obstacle with an if-then.
In one study, students who learned this completed more practice questions for an exam than students who did a control exercise.
Try this
Before you promise, name the one thing most likely to get in the way, and add "if that happens, I will …".
Source
Students taught mental contrasting with if-then plans completed more practice questions than a control group.
Duckworth, A. L., Grant, H., Loew, B., Oettingen, G., & Gollwitzer, P. M. (2011). Self-regulation strategies improve self-discipline in adolescents: Benefits of mental contrasting and implementation intentions. Educational Psychology, 31(1), 17–26.
A general finding about how people tend to work — not advice for your situation, and not a diagnosis.