Well, that's an exaggeration.
DD alone means nothing. It's just a representation of a volume.
DD has a lot of cultural meaning. Hollywood or porn or Cosmo (not really sure which) has us convinced that DD breasts are almost as big as one can get, second only to the unfathomable DDD. I mean how do those DDD girls even stand up?
She stands up just fine, because in the world of bras, DD and DDD are just the beginning. They are some of our most common sizes, and truthfully often the smallest we order a bra in.
DD also only means something in relation to the band size. Check this out:
In the first two pictures, both bras are DDs. No fancy camera tricks here- the black 38DD is a much "bigger" bra than the café 30DD.
In the second two pictures, the black bra is a 30C and is much smaller volume than the 38A in Café. Cup size means nothing without the band.
So look, if you're struggling to find your right fit, come see us. If DD doesn't fit, we have options all the way to O. P even in some brands. We can help. You are not defined by a size and the tag alone means nothing...