I absolutely don't like that man talking down to Sara, and as she said, that's his modus operandi to break "young girls" spirits (fucked up). HOWEVER, he was not entirely wrong about her character, her lack of ambition and lack of sincerity. It is obvious Sara's passion has long gone since her family's passing, so I see two options here:
a) Sara regains her passion and finds courage to live her life happily and without guilt (with Soojoon's support, obviously)
b) Again, with the power of love, self-healing, introspection and hopefully therapy (although I know it's not common in SK or is looked upon as taboo), she'll find her new path, abandoning the idol life and along it, that persona she hates that people (fans, staff and even past lovers) love.
HUMBLE OPINION
Am I the only one that wants to see Dawun as the bottom in this scenario???