title: Why does mongo not apply limit and skip before fetching
body: <p>I wrote a query in mongo db that uses an index (both for the query as the sort part). If I explain the query I get: </p>
  
  <pre><code>"cursor" : "BtreeCursor state_1_lastModified_-1",
  "scanAndOrder" : false,
  "indexOnly" : false,
  "stats": 
  "LIMIT" -&gt; "SKIP" -&gt; "FETCH" -&gt; "IXSCAN"
  </code></pre>
  
  <p>Why is mongo not able to skip and limit on the index before the fetch? 
  I know I could use a range query to avoid using limit and skip. </p>