Knowing what motivates you can be incredibly valuable, especially when it comes to starting your passion project that has been on the back burner for ages. Gretchen Rubin, author of The Four Tendencies: The Indispensable Personality Profiles That Reveal How to Make Your Life Better (and Other People's Lives Better, Too, places all personalities into four distinct categories: questioner, obliger, rebel, and upholder.
Questioners are motivated by the best possible choice. They have to know exactly what an expectation is and everything that it entails, and then decide that it's worth their time. They can be incredibly productive and effective, but they'll have trouble getting motivated to start a project if they're not 100% sure it's useful and not dumb. If this sounds like you, try breaking up your goals and expectations into little tasks with deadlines. It might help you take things a day at a time.
Obligers are motivated by other people's expectations. Give them a task and a deadline, and they'll get it done. Obligers do well in office settings and other workplaces with team supervision. They may feel lost when trying to meet their own goals and expectations, though, and often struggle to find their inner boss. If that's you, feel free to share your goals with a friend or mentor who will keep you accountable. You don't have to rely on yourself all the time.
Rebels are motivated by all expectations-- by resisting them, that is. They value their own freedom and independence, and feel motivated to do things that they're specifically told not to do. They can be constructively competitive yet often self-destructive, missing deadlines and goals simply to prove others wrong. Personally, I'm a rebel. I only feel motivated to do things when people specifically tell me not to do them. I'll even do the opposite of what I told myself to do! It gets exhausting.
If you're a rebel, try having conversations with yourself. Remind yourself that sometimes meeting the expectations of others fulfills your own goals, and they're just a tool to help you get there. Avoid being around too many rules and social conventions (unless your goal is to do the opposite!)
Upholders are models of the dream corporate employee: they meet any and all expectations. They meet deadlines, play by the rules, and do what they're told without much of an issue, regardless of whether their boss is hovering over them. The only problem with upholders is that they can be too stuck to the script (i.e. schedules and routines), and have a difficult time in an environment where things keep changing. Upholders should pursue stable work environments.
If you're not sure which motivation tendency describes you, take Rubin's online quiz to find out.