Stress
Technical writing can be difficult and boring. You may have to decipher indecipherable medical jargon for a piece on a medical experiment, or you may be the poor computer admin who has to type out a PeopleSoft training manual for a bunch of university staff members. It can also eat your life, if you end up on a project that requires a lot of overtime or working an abnormal schedule that includes nights and/or weekends
Finally, everyone will have an opinion about what you've written, and patiently handling all the comments, criticism, and advice you'll receive about your documentation may be the most difficult part of the job.