Of course an almighty God in general needn't be possible to prove (whatever that means in detail). It's just not a very plausible proposition and hence probably wrong. There are so many other unprovable things you don't believe which are more plausible. It's a matter of thought hygiene: If you believe everything you can't disprove, you end up with an infinite pile of contradictory garbage.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
