What is the single skill that is most important to an Internet Markete

Some warriors are complaining that they are getting information overload from reading tonnes of articles, wso and threads that they do not know where to start.

If there is one single skill an internet marketing should master, what should it be?

I hope to get the ball rolling by saying, I feel it is Copywriting.

A marketer should be equipped with certain degree of copywriting skill. Even through it can be outsourced, one need to be able to tell the different between good copywriting and bad one so that he/she can request it to be changed to what he see fit.

I recommend Gary Halbert letter, Influence: Science and Practice 5th edition and Ogilvy on Advertising.

What do you think?