Basically, things that build character are comprised of anything that is disagreeable. For some strange Calvinistic and/or Japanese reason, character cannot be built by winning a prize, taking a swim, or eating my delicious apple streusel cake. One must suffer to have character.
I doubt that this is true in general, but in specific, as it applies to writers, it is definitely true. It is not necessary for you to fulfill the Romantic ideal: a sensitive, unshaven (women too), starving creature agonizing in a garret. Yes, you will eventually get to do all that. But the real suffering, the real character building, comes not in the process of writing, which is sheer fun and therefore useless for building character, but in the process of sharing what you've written.
These are the writer's steps to building character:
Step 1: Don't publish too early. You have written a book. Don't get it out there. Instead, get it critiqued, as harshly as possible. You want to bleed.
Step 2: When you have bled enough, still don't try to publish. Write another book. Yes, that's what I said. Write ANOTHER BOOK. What kind of writer do you expect to be if you can only write one book? Then go back to your first book and revise it.
Step 3: Write short stories and articles. Get them critiqued. Bleed.
Step 4: Submit your short stories and articles to top-ranking magazines and ezines. You will be rejected. Bleed and revise. Submit again. Each time you get a rejection, re-read your work and revise.
Step 5: AGH! Somebody published your story! Your character is destroyed! Sadly, no. Read the published version. It's amazing how many mistakes you can catch after your story has been published. Ouch.
Step 6: At this point you have so much character you need a transfusion. Start submitting your book to agents. They will reject you. Each time you get a rejection, look at your query letter and revise it. Submit again.
Step 7: AGGHHH! An agent wants to represent you! Now, you're cooked. Don't get too comfy. She or he will want to take your manuscript and change everything in it. You have to decide what to change and what not to change. Your character is firming up nicely.
Step 8: You have followed your agent's suggestions - or not, as the case may be. And NOTHING happens! Not one single publisher is interested in your book. They say awful things about it. You have to decide if some of these awful things are true. They might be. Great character-building technique.
Step 9: AAAGGGGHHH!!! Someone wants to publish your book!! You are fried!! You thought the agent was harsh. Wait until you see what an EDITOR does to your manuscript!! It will be drawn and quartered before your very eyes. They will change your title. You will want to die.
Step 10: You now have character. Write another book. This time it had better be good.
(Repeat steps 1 through 10 as often as necessary.)
(Building Character was first published on Blogging Authors 11/1/12: http://www.bloggingauthors.com/)