See, neapolitan ice cream is made up of three flavours - vanilla, chocolate and strawberry - and the Trinity is made up of three aspects - Father, Son, and Holy Spirit/Ghost. But it's also a single block of ice cream, and the Trinity is a single thing. You have one ice cream which is also at the same time three different ice creams, and one God who is also at the same time three different things. And you can have a bit of each flavour/aspect, or combine the whole lot together.
There you go - mystery solved!