There’s a recurring debate in theatre about which job is the hardest: acting, directing, designing, stage managing, etc. I’ve tackled just about every job there is at least once, including the best job (fight director ) and the worst job (producer ), but there’s no doubt in my mind which is the hardest—playwright. 
As always, it depends on your metric. Tapping away on a keyboard isn’t nearly as strenuous as adding two dozen fresnels to an overstuffed grid, or as mentally taxing as committing 800 lines of verse to memory to play Richard III—and if you’re a costume designer, you’re probably rolling your eyes right now—but play writing is demanding in its own way.
Actors, directors and designers all get to start with a script. Playwrights start with nothing—just a blank page and an idea (and, if they’re lucky, a deadline, but that’s a topic for another post). Actors spend a month or two in rehearsal, but playwrights measure their effort in years.  And everyone but the playwright has the luxury of signing on to a show that’s already scheduled to go into production.  Playwrights, unless they’re working on commission, toil away on their own with no guarantee that anyone will ever even read their work, let alone see it performed.
On the other hand, if you make it that far, there’s nothing more rewarding than seeing your words come to life on stage in the hands of a talented and dedicated creative team. On the other other hand, there’s nothing more painful than when a director deliberately subverts your script for their own ends.
In fact, scratch what I said earlier about fight directing and producing. Playwriting isn’t just the hardest job in theatre, it’s the most Dickensian—the best of jobs and the worst of jobs, the job of wisdom and the job of foolishness, of belief and incredulity, of hope and despair …
1. Fight directing is the biggest bang for the buck in theatre. Fight directors deliver huge impact to the production with (relatively) little rehearsal time. They get to work on the most exciting scenes in the show and only those scenes. They can buy swords and write them off as a business expense.
2. Producers shoulder all the responsibility for a production with very little agency—that’s down to the director—and none of the glory—which goes primarily to the actors. True, they rake in those sweet, sweet box office receipts … if there’s a profit. More often they’re trying to minimize the losses. It’s a terrible, horrible, no good, very bad job in every way but one: producers can make shows happen. Want to (make a weird show happen)? Secure the rights, book a venue, hire a director, and you’re in business.
Most people should never even consider producing except as a hyphenate—actor-producer, writer-producer, director-producer—in which case it can enable opportunities no one else is willing to give you. Want to play across type, gender, race or age? It’s your show. No one in your town is producing scripts that represent your demographic, reflect your culture or speak to your generation? The buck stops with you.
As in the self-publishing world, a lot of godawful crap gets self-produced. That’s okay. Established theatres have churned out their share of godawful crap as well. Remember Sturgeon’s Law—ninety-five percent of everything is crap. Rise above.
3. Okay, that wasn’t too hard to guess. This is a blog about writing, after all, not theatre (although some theatre creeps in from time to time).
4. Terry Rossio has an outstanding column on the relative opportunity cost—which he calls time risk—of actors and writers. It’s geared toward Hollywood, but the same principle applies to the theatre.
5. Which, admittedly, is its own kind of challenge. A long rehearsal process and extended run can play havoc with work schedules and social commitments and lesser obligations like eating and sleeping.
6. This is a spurious footnote, not cited above. I just felt obligated to mention that more than half of this post, by word count, is foot notes.