The Periodic Exams
While I could not be online for a month, tons of new questions have been added routinely. So, I feel like I can hardly pass the exam.
If the system allows me to try again with a different set of questions after failing it (like the FCC exams in Amateur Radio licensing), I may still have a chance. However, current TMO has no such flexibility. "If I feel like it's done, then it's done" It is true but...