Everyone does it.
But it is all about tailoring what you want to make to how you work as a person.
If you're easily intimdated by large amounts of work, then keep your projects small and concise.
If you're bored by smaller projects, then create a challenging one that is a bit bigger.
If you have a bad attention span, make projects that can be completed in a short amount of time.
Find inspiration and people who can help inspire and motivate you. Otherwise you'll feel like no one may appreciate your work.
Over the past 10 years I have started about 6 different levels and not finished most of them or scrapped them or deleted them. It happens to everyone.
Also be smart about what you do and managing yourself.
Back up files every day, use a local SVN, make a list, get a white board.
If you aren't managing your content creation, then your mod/level/what ever will probably not see the light of day.
Just stay focused and make what you need to make to complete your project.
My 2 cents.