The problem being addressed is that asynchronous coding in JavaScript results in the Pyramid of Doom. To explain, let's reiterate the example Ryan Dahl gave as the primary Node.js idiom:

db.query('SELECT ..etc..', function(err, resultSet) { 
   if (err) { 
      // Instead, errors arrive here 
   } else { 
      // Instead, results arrive here 
    } 
}); 
// We WANT the errors or results to arrive here 

The goal was to avoid blocking the event loop with a long operation. Deferring the processing of results or errors using callback functions was an excellent solution and is the founding idiom of Node.js. The implementation of callback functions led to this pyramid-shaped problem.  Namely, that results and errors land in the callback. Rather than delivering them to the next line of code, the errors and results are buried.

Promises help flatten the code so that it no longer takes a pyramidal shape. They also capture errors, ensuring delivery to a useful location. But those errors and results are still buried inside an anonymous function and do not get delivered to the next line of code.

Further, using Promises results in a little bit of boilerplate code that obscures the programmers intent. It's less boilerplate than with regular callback functions, but the boilerplate is still there.

Fortunately, the ECMAScript committee kept working on the problem.