Everything you are and everything you will be exists inside of you ready to burst. The amount of potential inside of you is immeasurable. There is no way that anyone can tell you the limits of your potential. Anyone who tell you otherwise is wrong.
If people tell you that you can't achieve your goal, they're wrong, even if they're well-intentioned. You may not be able to do it now, but that doesn't mean that you won't be able to do it at another time. By then you'll be smarter, wiser, and more experienced. Next time will be better.
Unfortunately, you'll never fully be able to control the situations you're placed in. Life may unexpectedly hit you with a curve ball. What you can do is control how you react to the situation you're in. You can choose to be proactive and positive, or you can choose to give up. Don't give up.
You can do it. Keep going. The potential power rests inside of you. It's time to bring it out.