"It wouldn't work."
"I'm not good enough.""I could never afford that."
"I can't..." etc.
If these are the things you keep telling yourself, YOU'RE MAKING THEM TRUE.
You simply won't take the steps to achieve something if you don't believe it's possible in the first place. This just might be the only thing stopping you from getting what you truly want out of life.
You get what you look for.
Your subconscious mind doesn't argue with you. Whether you tell it something good or bad, true or untrue, it goes to work for you to find confirmation of what you already believe. (The best part, for a major skeptic like myself, is that there is SCIENCE behind this!)
If you're looking for reasons you can't do something, you'll find them - there are flaws in everything, and there will always be obstacles. Anyone can easily find an excuse. That's what most people do. If you focus on what's possible for you instead, you'll find opportunities. That's what successful people do.