When do writers give up writing because; after receiving hundreds of postage-stamp rejections, all impersonal form rejects--that they don't have the skills or creativity to write queries that pop? That they finally understand that what they write is of no interest to readers? That all the loneliness combined with social dysfunction-ability makes them paranoid or socially-pathological? That they become anorexic from malnutrition? That they are broke and can't pay the rent? So forth and so on.
Do they give up writing because of their lack of writing skills, or because of extenuating circumstances like standing on a street corner with a sign that reads; WILL WRITE RESUMES FOR THE USE OF YOUR LAPTOP?
Do they not give up writing and write one continuous line like Jack Torrance did in The Shinning; HERE SITS AN UN-GIFTED WRITER 1980 - 2010.
Do they give up writing because either their partners or spouses stand behind them holding a knife or gun?
Do they not give up writing and just write garage sale notices or obituaries?
Do they give up writing because their inner-voice screams ninjas are fake, dental floss is a mistake?
Do they not give up writing because there just isn't enough vampire stories?
I can think of thousands of reasons to give up writing, some funny and most not so funny, but the one main reason writers should continue to write, if they don't become published, is to write for themselves. Personal stories can be historic family sagas, stories about your childhood, exploits in your profession, epics about a life-time of financial investments, a tome about failures and successes, grievances and justice, accusations and praise, objections and approval, unfairness and equality covering many of the events in your life. If writers pursued such stories their families' appreciation for them would sky-rocket.
Just remember, do not give up writing. The entire process can be therapeutic. Yes, ninjas are real and dental floss use is mandatory.