According to reports when it was announced that Fidel Ángel Castro Díaz-Balart AKA "Fidelito" had died, Cuba’s state TV said Fidelito “had taken his own life after suffering with deep depression which doctors had been treating him for over several months”. Fidelito was “said in recent years to have grown weary - both of living in his father's shadow and having been sidelined from Cuban decision-making on energy resources.”
"Fidelito was a nuclear physicist, trained by the former Soviet Union. His ideas for developing renewable energy on the island were not incorporated into state policy" so that was probably very disappointing to him. Also, without proper treatment, a person suffering from severe depression has trouble just functioning from day to day and can’t possibly be expected to do a whole lot more than that.