Max efficiency in Map, question from website tuterial

[behzadkh]

Any one know why there is a max of efficiency in the first line and it does not in the second line

mymap.insert (it, pair<char,int>('b',300));  // max efficiency inserting
mymap.insert (it, pair<char,int>('c',400));  // no max efficiency inserting 

// map::insert
#include <iostream>
#include <map>
using namespace std;

int main ()
{
  map<char,int> mymap;
  map<char,int>::iterator it;
  pair<map<char,int>::iterator,bool> ret;

  // first insert function version (single parameter):
  mymap.insert ( pair<char,int>('a',100) );
  mymap.insert ( pair<char,int>('z',200) );
  ret=mymap.insert (pair<char,int>('z',500) ); 
  if (ret.second==false)
  {
    cout << "element 'z' already existed";
    cout << " with a value of " << ret.first->second << endl;
  }

  // second insert function version (with hint position):
  it=mymap.begin();
  mymap.insert (it, pair<char,int>('b',300));  // max efficiency inserting
  mymap.insert (it, pair<char,int>('c',400));  // no max efficiency inserting

  // third insert function version (range insertion):
  map<char,int> anothermap;
  anothermap.insert(mymap.begin(),mymap.find('c'));

  // showing contents:
  cout << "mymap contains:\n";
  for ( it=mymap.begin() ; it != mymap.end(); it++ )
    cout << (*it).first << " => " << (*it).second << endl;

  cout << "anothermap contains:\n";
  for ( it=anothermap.begin() ; it != anothermap.end(); it++ )
    cout << (*it).first << " => " << (*it).second << endl;

  return 0;
}