In a traditional classroom, the instructor can look around the room and tell when students do not understand the material. When the class signals that they need to slow down, he will. And when he sees that he is belaboring the point, he can speed things up. He can also change the way he is teaching on the spot, providing the appropriate outputs to fit various learning styles. For example, when students cannot understand a verbal description, he can draw a diagram. Online learners have no face time with the instructor.
If you learn best through the inputs and exchanges with fellow students, online training may prove challenging. Humans crave social interaction. Even introverts are social creatures. The social aspects of a traditional classroom can make the experience more engaging. Some online learners may find online classes boring and have difficulty concentrating.
Online classrooms can be frustrating if you lack the ability to use the technology. In addition to navigating the screens, you may need to submit work to the instructor, ask questions in a forum, or collaborate with a virtual work group. Also, computers tend to lock up, lose information or otherwise fail to cooperate at the most inopportune times. (Do consider, however, that learning new technology is not a disadvantage in the long-run.)
Online discussions can be slower than face-to-face interactions. Some online classrooms offer instant messaging capabilities and chat rooms, but this isn't always the case. If you require instant feedback, online classrooms can hinder progress.
Children, pets, home chores, work responsibilities, a too-busy life--the very reasons that prompt you to take online classes may be the same reasons that give you pause. The distractions of day-to-day living can make online learning less effective. In online classrooms, you are able to proceed at your own pace. This makes it even more tempting to mismanage your time and let distractions take over.