If you are passionate you can still have excuses for passing in one day not doing it, you can still stop, you can still pretend that you love what you are doing even if you somehow feel a little bit low or unmotivated. But everything is still good, of course you will come back to what you are doing, your motivation will come back again, the love for your work will go strong again. That is why it is called passion.. it never dies, your creativity keeps coming back even if you are doing it for a very long time. You may get tired but you will never leave it.
But obsession is different. Obsession means you are relentless, it means you are willing to die for it. It means you are willing to live for it and work for it 24 hours a day. You can't stop thinking about it, you want to do everything for it. Obsession is a mental illness but if you are obsess with your dreams and you use it in a positive way then for sure you will become successful.
Passion means giving your best for something but obsession means giving your life for something, obsession is a powerful tool to become successful rapidly. Passion will create masterpiece while obsession creates miracles, it conquers impossible things. It makes the hard look easy, it makes the abnormal look normal.
If you are obsessed you will see no obstacles, you will only see way, you will only see a path that you think will make you successful. And even if that path is wrong... you will try another path, you will try over and over again until you become successful. Obsession can break any wall that is stopping you from seeing your dreams. Obsession is far way better than passion.