It becomes impossible to transclude (if you write <<some variable>>, nothing will appear). This is because words after the first space in the angle brackets are treated as parameters rather than as part of the name of the variable. This will make sense in a moment when we talk about Procedures.

You might wonder if you could say <<"the eis">> to refer to a variable name containing a space, by analogy to the way you can include multiple words in the value of an HTML attribute, but this isn't valid syntax.