Essential Startup Skills?

What do you think are the key skills startups should master to maximize their chances of success?

Premise

As solo-entrepreneurs we have to do almost everything in the beginning, so it's probably a good idea to get a decent understanding of all the key skills.

Here is my list. Please let me know if I am missing anything or you disagree.

Lean Startup - understanding MVP and the importance of pivoting to customer feedback

Copywriting - convincing people to buy from you

Content Marketing - getting attention cost effectively

SEO - Getting found in search

Paid Advertising - driving traffic cost-effectively

Analytics - knowing where your customers are coming from and what they are doing on your site

Networking - connecting with people to improve your future opportunities

Sales - the ability to generate business for your company, attract employees, motivate workers, etc.

Is there anything you'd add or subtract there? Thanks, John