You believe in gravity because you experience it.
Say i experienced gravity, but the vast majority of the human animals on this planet did not, or could not. Then it would be safe for me to conclude that my experience of gravity is merely a figment of my imagination, as it does not pertain to everyone... just myself, within my own limited mind and experience.
Except, that with gravity, we all know that everyone whom resides within this reality can, and does experience it every day, every moment of every day it effects us, all of us. We can watch it as we watch the planets revolve around each other, as black holes suck in every piece of matter that comes too close, as we watch water fall to the ground from the sky, as we watch the rivers flow down the mountains and not up them. As we throw a baseball or football, as we drop our phones, as we drop our TV remote controllers on our feet and wince from the temporary pain.
If i were to believe everything i experienced, i would inevitably become disillusioned and maybe even insane, because as we all know, through optical illusions that our brains fool us ALL the time. The only way to be sure of something is to show others, allow them to see and to confirm whether or not our conclusion is sound, or just a figment of our imagination. To help us figure out whether or not we should continue to be skeptical of a conclusion we have come up with, or be verified in our thinking.
If we cannot share our experience with other people, how can we be sure it is not just a figment of our imagination? How? By pleading with ourselves? By continuing to tell ourselves;
"It doesn't matter if no one else sees the things i see, or experiences the things i experience, i know it is true because i feel it and, and i believe it! I don't care if no one else can!"
-that does not sound like a way to get to the truth about something, that does not sound like a way to get past doubting our own ideas and conclusions we come up with. That, to me, sounds like a scape goat, a way to believe something just because we want to regardless of what anyone else says, regardless of what the mass population says.
Don't get me wrong, i would love to believe (to feel sure of the truth of) in the idea of us having an eternal soul, of a part of us continuing to exist after we die. A part of me wants to believe that so much. But i can't, even if i have had spiritual experiences that attempt to explain to me that i do... because i know my mind is fallible, it is prone to error, and if i can't show anyone else how am i supposed to be certain that my experience was anything but a figment of my imagination or a dream?
I can't be certain i have a soul, i have to be honest with myself. I know that no matter how badly i want one, no matter how much i believe, it doesn't make it so, it doesn't mean i have one... i could be wrong. The truth is;
That i don't know. I don't know, and i am not afraid to say it or tell people that.
The skeptics here are merely trying to make one point, and one point only; How can you be certain, how can you be absolutely sure you have a soul or that souls exist without being able to show others? Now understand that i am absolutely not saying that souls do not exist, because like i have stated before, I DON'T KNOW. But neither do you know for sure, or anyone else on the planet for that matter, because the idea of souls has not yet been proven beyond a reasonable doubt throughout the whole population of human animals on this small rotating rock.
To say you are absolutely sure that souls exist, only allows us to see your desperation that they do exist... when anyone with a basic understanding of reality can tell you honestly... how can you be so sure??? And when you do not have a sound answer, we can look in your eyes and see the doubt, but you have been hiding from it all the while.
It is ok to doubt, you can still doubt and hold onto a belief. I believe this is a dream, but all within the understanding that i do not know if it is or not. It takes courage to doubt our most cherished and desired beliefs... but in order to get to the truth, we must at one time in our lives doubt everything.
It is ok to say; "I don't know" "I am not absolutely sure, but i think it's true" "I could be wrong, but i am going to believe it anyways" Those are honest answers, honest words.
To say you know for certain, for sure, only shows the rest of us your desperation brought from the fear of being wrong.