Quite simply, Arkadina is completely self-absorbed. She is rich, has an estate, has a lover, and does not care squat about her son, Konstantine. How do we know Arkadina is cruel? Well, Konstantine writes a pretty decent play that is both esoteric and full of symbolism, but Arkadina is not impressed at all, calling the play "decadent." Due to Arkadina's bad review, her son is devastated. All Arkadina cares about is impressing Trigorin, her lover, who is also selfish. 

One must admit, however, that it probably did not help the relationship much to try and kill himself and then put down Arkadina before she leaves during the third act. Still, the readers get a little more clarity about her cruelty to her son when she returns, an older woman, and it is her son who is the popular playwright. Her acting career has diminished. We can see, then, that Arkadina is actually jealous of her own son, who has the greater talent and the youth to use it.

In conclusion,  it is important to realize that neither character achieves his or her dreams. Arkadina is desperately trying to hang on to acting (and Tigorin) and Konstantine eventually kills himself after being rebuffed by Nina.