Everything is in your realm of possibility
While it may sound cliche, there truly aren't many dreams that are impossible. While I acknowledge that privilege plays a huge role in giving some people a head start, everything that exists in this world is yours for the taking. The only thing that stands in the way is the limitation you put on yourself... and sometimes, time. Because, sure some goals are naturally going to take longer than others to achieve, due to the gap between where you currently are and where you want to be.
For example, if your dream is to go into outer space, but you've never studied astrophysics, it's probably not something you're going to be able to tick off the list tomorrow. But, if someone else has achieved it before, know that it's within the realm of possibility for you too.
It never harmed anyone
You'd be hard-pressed to find any downsides to dreaming bigger. Because honestly, what's the worst that can happen. Someone might judge you? Okay, well as we've already established, that says far more about their narrow perspective than it does about you. Or, maybe you'll become disappointed in yourself for not achieving that goal? Perhaps, with a simple mindset shift, you can live with that. Plus, just because you haven't achieved it yet, doesn't mean you never will. Rather than wondering "what happens if I fail?", ask yourself "what happens if I succeed?" 99.9% of the time, the rewards far outweigh any perceived risks.
It's contagious
When we dream big, it takes the people around us to stand up and pay attention. There will likely be just them projecting their insecurities onto you, there will likely also be just as many who are inspired by your boldness and think "wow, maybe I'm aiming too low with my goals". When we encourage others to raise the bar and expand their horizons with their dreams, it's always a good thing.
Even if you 'fail', you win
A quote by Leslie Calvin Brown says "shoot for the moon - even if you miss, you'll land amongst the stars". I think this really sums up what is so powerful about pursuing so called 'impossible goals'. Because even if you don't achieve that particular goal within your designated time frame, you've likely gotten much, more further than you would have if you had set a more realistic target. After all, you've had to take 10 x the amount of action that you would otherwise, and that's always going to get you much closer. You also need to look at the person you've had to become in the process of striving for that goal. Perhaps you're stronger, more confident and resilient. That transformation is far more poignant than the specific goal itself.
It helps you take more action
The idea of impossible goals is at the heart of the book 'The 10 x Rule' by speaker and entrepreneur Grant Cardone. His rule is simply: If you set targets for yourself that are 10 x bigger than you actually achieve, then it forces you to take 10 x more action than what you would have otherwise. And, Grant teaches, this is the level of action that is required to achieve remarkable things. The funny thing is, when we set smaller goals, we actually become more paralyzed by fear of failure - because we know it's within our reach, and that it's our own fault if we don't achieve them. But, when we set targets that we believe are outside the realm of possibility, we're more likely to think "hey, may as well give it a shot - what do i have to lose?"