No one ever says, "She's weak. That's why she goes to the dentist to get her teeth cleaned." After all, we appreciate people who take care of their teeth.
People don't always get the same respect when they choose to take care of their minds. There's a stigma attached to therapy, and some people still insist that seeing a mental health professional is a sign of weakness.
But the truth is, it takes strength to ask for help. And it takes strength to admit that you don't have all of the answers and want to invest time into improving yourself.
A mental illness, like depression, isn't a sign of weakness any more than a physical illness, like seasonal allergies. While developing mental strength can improve mental health, it doesn't guarantee you won't ever develop an illness.