To be successful in an online course you need to be motivated and self-disciplined as well as able to advocate for yourself if you are having difficulty with course material.
Online courses typically require online collaboration with classmates. Additionally, technical difficulties are quite common with online courses (e.g. the requirement to download certain software). It is important that students feel comfortable trouble-shooting, acquiring support, and experimenting with different technology if they are to take an online course.
If you prefer "hands on work" or physical interaction with classmates and your teacher over primarily a visual and auditory learning environment, then online courses may not be best for you.