What is truth?
I'm sure there are better explanations, but I consider truth to be any proposition for which there are examples in the world, and for which there are no counterexamples. The truthful proposition must be consistent with the real world. The more examples that exemplify the proposition, without a counterexample, the more confidence we can have that the proposition is true.
Take for example the rising of the sun. It happens every twenty-four hours, give or take a few seconds. I'm in my late fifties, and I can say that there's never been a day that the sun did not rise. Over 20 thousand times the sun has come up in the morning - not once did it not come up. I consider it to be true that the sun always comes up every day. Combine my personal observations with those of the billions of people alive today, and my confidence level increases several billion-fold. Sixty or eighty trillion observations that confirmed the proposition that the sun comes up every day, without a single counterexample. We can extend this to include all people who ever lived ... maybe 106 billion since homo sapiens emerged as a species. We as a species have pretty solid confidence that the sun rises in the morning.
Let's assume a different scenario. Let's assume that ghosts are observable in the real world. I personally have never observed such a thing. That doesn't mean they don't exist. I haven't seen a single serving president of the United States either, but I'm confident that they do exist based on numerous reports from allegedly reliable contemporary and historical sources. Do I have the same sort of confirmation from reliable contemporary or historical sources that ghosts exist? No.
Contrast scenario A - that the sun comes up in the morning - with scenario B - that ghosts are observable in the real world. Just using our contemporary observers, the consistently rising sun has approximately 70 trillion out of 70 trillion observations - without exception - that support the proposition. It could be true that one day the sun will not rise, so let's assume that in the next 70 trillion separate observations, one day the sun does not come up. All of us will notice this - unless it's the day after Saint Patrick's Day, in which case several million folks in the U.S. and Ireland (at least) will be extremely hung over, and may not be conscious or competent to make an observation that day. But on one day, we all see that the sun did not rise.
If, on the day the the sun doesn't rise, we then can say that yes, that does indeed happen. The best we might be able to do is to project that the event "the sun does not rise one day" now might conceivably happen once every five or ten thousand years - or whatever duration we can use as a yardstick.
Turning to scenario B - we - as a species - have no credible observations of ghosts. What's more, a single credible example doesn't increase our confidence much. If one person in 7 billion observed a ghost, and it could be verified that such a thing was probably true, without a second similar observation to lend confirmation, there is not much evidence to move the needle from "it is extremely improbable that ghosts can be observed in the real world" to "it is slightly improbable that ghosts can be observed in the real world".
I've said it before, and I'll say it again, that gods, and specifically the Abrahamic God Yahweh, are specialized and highly specialized cases (respectively) of the supernatural. Ghosts are less specialized examples of the supernatural - they are, presumably, not capable of creating the universe; nor supervising it; nor intervening in the lives of its inhabitants; nor judging the conjectural souls of these inhabitants when they expire; nor consigning these conjectural souls to places of punishment or reward for all eternity - places that are not observable nor verifiable to the inhabitants of the universe; nor maintaining these places of reward and punishment alongside, but completely undetectable from the universe in which the real inhabitants live their brief lives. So gods, and specifically the god Yahweh, are even more improbable than ghosts.
There's just no reason to believe that such a being exists.