Blender was not designed with 3d printing in mind, so you can easily end up with models with intersecting triangles, flipped normally, non manifold edges, and single width polygons, and while some slicers can handle some of those things, the single width polygons will make that part of the model unprintable (it's only a 2d object with zero thickness at that point). So, just though you're great at creating a realistic-looking model of a human, dragon, dog, cat, or anything, it doesn't imply it'll be printable.
