Why can't I grasp the fact that time had/has no beginning?
Time never began happening, it's always been there. The fact that time will never end, is easier for me to understand, probably because it is still to come. What was there before earth? There could have been billions of intelligent species before us, and there probably will be billions more to come.
Beginning and end are man made terms.
Not everything can be proven by mankind; this is why I don't find it hard to believe in a superior being.
Maybe it's better not to prove everything, because it mostly just leads into disappointment.