It is important that your dream be realistic and you are willing to do the work. If you want to run a marathon next week but you are 500 pounds and never ran before-it is not going to happen. But, if you are willing to loose the weight, begin a fitness routine that includes running, at some point you will be able to run a marathon. Achieving your goal has nothing to do with other peoples opinion and everything to do with you.
Encouragement comes from within. If you do not believe in yourself it does not matter how awesome other people think you or your idea is.
Establish your goal, commit to doing whatever it takes to accomplish it and then do it.