What does the quote, “Keep your face to the sunshine and you cannot see the shadow," attributed to Helen Keller, mean?

The beautiful sunflower is well-known for following the
path of the sun. From the east in the morning to the west at night, the sunflower
repeats this process each day with the bloom always facing the direction of the
sun. 

Helen Keller, left blind and mute after an illness at
the age of nineteen months, proves that attitude, and a refusal to accept life in "the
shadows of the prison-house," changes insurmountable challenges into awe-inspiring
achievement. She wrote The Story of My Life so that she could
contribute to society and help others learn from her story which reveals her desperate
attempts to communicate and her many failures and confrontations en route to
overwhelming success. In The Story of My Life, Helen compares her
life, before the discovery, with Annie Sullivan's help, of words like "W-A-T-E-R," to a
prison-house from which there is no release. Helen refuses to dwell on the
energy-sapping, unfulfilling moments of her life, because she knows only too well, how
much easier it would be to allow her disability to overwhelm and define her. She
mentions various challenges but chooses to  use them to help her understand her
otherwise, "silent, aimless, dayless life." She compares herself to a ship "without
compass," before the arrival of Annie Sullivan and recognizes Annie's arrival as "The
most important day I remember in all my life."

There is a
lot of poetic language attributed to Helen Keller which reveals her in-depth
appreciation for life and is especially remarkable as she is able to describe nature,
events and people in ways that even sighted people can never hope to strive for.
Remaining hopeful and always believing in others and in the power of communication
which, "awakened my soul, gave it light, hope, joy, set it free," ensures that she, even
in the twenty first century, inspires people. The sunflower grows to an enormous size
and shadows from other, equally-huge, sunflowers threaten to reduce the available light.
However, the sunflower still "looks" for the sun, refusing to remain in the shadows.
Helen Keller, too, has created a legacy and encourages others to always "look" towards
the light in attempting to make the best of any situation. The quote, whether Helen's
own words or not, aptly describes her philosophy.