Any kind of habit, whether good or bad, is self-sustaining.
For example, if you begin to go out for runs every day, it becomes easier over time to stick to the routine. Running also releases endorphins, which makes you want to exercise again.
But on the other hand, if you have a bad habit (like for example, overeating), the same endorphins that would have motivated you to run, will now be acquired from eating food instead. This means that to get your ‘happy fix’, you will raid the cupboard instead of working out.
There will be a similar effect when you are trying to achieve a goal.
If you reach the goal, then you get a sense of achievement which makes you feel good, and this in turn motivates you to set and reach more targets. However, if you don’t achieve the goal, then you can become unmotivated and feel bad about yourself, which often leads to thoughts such as, ‘why bother?’.
The more goals you have to work towards, the less likely you are to achieve them. But the fewer, more targeted, and more achievable the goals are, the more chance of success you have.