Patience is a virtue.
How many times have you heard that in your life? Truth is, patience is one of the most important skills you can have in any career. As a writer (especially if you're choosing to go the traditional publishing route) it's a make or break kind of thing. You can send your manuscript out into the world, but you won't get a response immediately.
It could take months. And in that time, you have to wait patiently. No one wants to be harassed -- sending daily emails, "Did you read it yet?" is only going to annoy an agent or editor.
If you're constantly stressing about hearing back from agents, or looking at how many people have visited your blog or bought your book on Amazon, you're going to be missing out on the most essential part of your career. Writing.
Of course you have to market yourself. Of course it matters how many copies of your book are selling. But these things are only a part of your job. Be patient. The books will sell. In the mean time, try creating your next big show off piece.
There is always going to be something to wait for in your writing career. Why not make use of that time while you can?