There's a fine line between ambition and delusion.
I'm hugely in favour of the former. I've tried the latter, in all kinds of ways (like when you think you have this great business idea and no matter how hard you try nobody - and I mean nobody - cares? but you keep trying anyway and it keeps not working? yeah that's painful), and I don't recommend it.
One of my favourite writers, Seth Godin, has a splendid little book about this, hoping to teach all of us to recognize the difference between "I need to push juuuuust a little harder and it'll work" and "this is doomed, abort". If you're not sure what to read next, try that one. It might even help you with those resolutions.