It is true that most of the people fail in online marketing. There are several reasons of failure the main reason they don't want to learn but they want to earn only.....
Other reason is there is too much scam in online business, you should have ability to recognize them and choose the right way to making money online.
Discipline is also very important, if you got some clients and you are not delivering on time, then it may not help you further for getting work from the same client.
Your communication skills should also be good, if you are in freelancing..