A task will expand to fill the time available.AKA Parkinson's Law
So how are we expected to complete tasks and projects with no deadlines?
Especially if you're not doing something for anyone else, how do you stay motivated?
You can try and set a personal deadline, but chances are you'll just not pay attention to it. Instead, involve other people. Get your friends to chase you up on your deadlines, or, if you're still struggling, have agreements where if you miss the deadline, you'll do something for them, like have to buy them a meal or sing an embarrassing song at a kareoke.
When there are consequences for missing your deadlines, you'll likely start paying more attention to them.
Another common problem is having the deadline be for the whole project or task. This is often overwhelming, and can be overcome by splitting it into smaller tasks.
If you're writing a book for example, you may consider writing the skeleton for a core plot point as a sub goal. Maybe you need to flesh out a character, or even just round out a chapter.
In fact, one sub goal can even be figuring out what all the sub goals for a particular point may be.
Keep track of your sub goals, and your progress on them. You'll want to celebrate the completion of each goal, and counting these successes will help you see your overall progress, which can help with motivation too.
There are various tools available to help motivate you. Duolingo is a great way to learn languages, but no one can save you if you don't keep up with your lessons.
A far less aggressive way to help prioritise would be the Finch app, which helps with self care, including completing your own goals.