As a personal perspective, I don't tend to believe that mastery of a programming tool is nearly as important as mastery of the codebase and problem domain you're working on. But there are some developers who just don't want to learn the codebase or what other developers are doing.

Take Jessica's latest co-worker, which is similar to some previous co-workers. In this case, there was a project in flight that was starting to fall behind schedule. Management did what management does in this situation: they threw warm bodies at the project and ensured that it fell further behind.

Brant was one of those warm bodies, and Brant did not want to learn what was already in the code base. He was going to do part of the JavaScript front end, he was going to rush to get it done, and he was going to copy-paste his way through.

Which lead to this:

function setMailingsReceivedCountLabel(e)
{
  // Implement sting prototye format so that we can use string token replacement
  if (!String.prototype.format) {
    String.prototype.format = function() {
      var args = arguments;
      return this.replace(/{(\d+)}/g, function(match, number) {
        return typeof args[number] != 'undefined'
        ? args[number]
        : match
        ;
      });
    };
  }

  // Get values
  var recordCount = $("#mailingsGrid").data("kendoGrid").dataSource.total();
  $("#Mailings_Count").text("(" + recordCount + ")");
}

Now, a format method for strings is a useful function. It's not wrong to implement your own- you can't rely on template literals being supported by every browser. In fact, it's such a useful function that Jessica and the team had already added one in a generic file of utility functions. A more robust one, coupled with some unit tests, and y'know, the one you should use.

Brant had no interest in learning that there was already a function which did what he needed, so instead he implemented this one. In fact, he copy-and-pasted this blob into any method he wrote that might potentially do any sort of string formatting. I stress "might potentially", because as you can see, this method doesn't actually use his format method.