She is a sensitive and emotional young woman who is easily overwhelmed by her feelings. This is evident in her interactions with Hamlet, where she is often unable to express herself clearly and is easily manipulated by him. She is also unable to deal with the death of her father, which sends her into a state of madness and ultimately leads to her death.
Ophelia's inability to cope with her life is likely due to a combination of factors, including her upbringing, her personality, and the circumstances of her life. She is raised in a highly patriarchal society where women are expected to be subservient to men. This stifles her own voice and makes it difficult for her to assert herself. She also has a natural tendency to be gentle and yielding, which makes it difficult for her to stand up for herself or to deal with difficult situations.
The circumstances of Ophelia's life also contribute to her downfall. She is caught in a love triangle between Hamlet, Laertes, and Claudius, which puts a great deal of stress on her. She is also unable to escape the expectations of her society, which further limits her ability to cope with her life.
Ultimately, Ophelia's major weakness is her inability to cope with the stresses and demands of her life. This leads to her madness and eventual death, making her one of the most tragic characters in the play.