Friends and relatives typically don’t realize what a bind they impose when they ask a professional writer to read their work.  F. Scott Fitzgerald shows how to tell the truth gently.  He also tells the truth about the sources of writing that matters.
Dear Frances:

I’ve read
the story carefully and, Frances, I’m afraid the price for doing
professional work is a good deal higher than you are prepared to pay
at present. You’ve got to sell your heart, your strongest reactions,
not the little minor things that only touch you lightly, the little
experiences that you might tell at dinner. This is especially true
when you begin to write, when you have not yet developed the
tricks of interesting people on paper, when you have none of the
technique which it takes time to learn. When, in short, you have only
your emotions to sell.

This is the experience of all writers.
It was necessary for Dickens to put into Oliver Twist the child’s
passionate resentment at being abused and starved that had haunted
his whole childhood. Ernest Hemingway’s first stories “In Our
Time” went right down to the bottom of all that he had ever felt
and known. In “This Side of Paradise” I wrote about a love
affair that was still bleeding as fresh as the skin wound on a

The amateur, seeing how the professional having
learned all that he’ll ever learn about writing can take a trivial
thing such as the most superficial reactions of three uncharacterized
girls and make it witty and charming—the amateur thinks he or she
can do the same. But the amateur can only realize his ability to
transfer his emotions to another person by some such desperate and
radical expedient as tearing your first tragic love story out of your
heart and putting it on pages for people to see.

That, anyhow,
is the price of admission. Whether you are prepared to pay it or,
whether it coincides or conflicts with your attitude on what is
“nice” is something for you to decide. But literature, even
light literature, will accept nothing less from the neophyte. It is
one of those professions that wants the “works.” You
wouldn’t be interested in a soldier who was only a little

In the light of this, it doesn’t seem worth while to
analyze why this story isn’t saleable but I am too fond of you to kid
you along about it, as one tends to do at my age. If you ever decide
to tell your stories, no one would be more interested

Your old friend,

F. Scott Fitzgerald

I might say that the writing is smooth and agreeable and some of the
pages very apt and charming. You have talent—which is the
equivalent of a soldier having the right physical qualifications for
entering West Point.

From F. Scott Fitzgerald: A Life in Letters: A New Collection Edited and
by Matthew J. Bruccoli.