How do you know if you are being delusional in what you want in life and your dreams,or if you believe that?

they can happen even though others think its delusional,should you still go for it and fight for the life you want to live and do everything to achieve that to prove it to yourself?how can you distinguish if you are believing in a fantasy,or if it can actually happen and materialize if you put the work in towards it all the time? even if others think you are being unrealistic your thoughts please thanks