Among other ironies in the play, Lear's tragedy is rooted in these two.
The daughters whom Lear loves and trusts the most and to whom he gives up his kingdom are the daughters who love him not at all and who betray him completely. Goneril treats her aged father with contempt, excercising the very power he gave her to abuse and humiliate him. When Lear turns to Regan for aid, she instead supports her sister in this cruelty. Because of the betrayal of these two daughters, Lear ultimately suffers beyond endurance and slips into madness--not the comfortable old age he believed he would enjoy with his two loving daughters caring for him.
The second basic irony in the play involves Cordelia. As the daughter who loves her father the most, the one who loves him enough to tell him the truth, Cordelia is disinherited and banished from her own country. Lear banishes Cordelia out of towering ego and foolish pride. It is Cordelia, however, who treats her father with tenderness and unconditional love at the end of his life, and it is Cordelia's death that plunges Lear into his deepest agony.