Just a personal observation. When I converted to Catholicism some 10 ago I remember thinking that the hardest thing for me would be buying into the doctrine of transubstantiation. When our parish priest explained it to us though it was so succinct and crystal clear to me that I have never had a doubt since. It is one of my best memories from RCIA.
(Having some liberal nun with the title “Diocesan Director for Social Justice” tell us that Nike tennis shoes were evil was the worst)