title: jsonschema validator error message include the whole schema
body: <p>I have a doubt about the source code of jsonschema validator:, I'm checking the validators.py file,  and found  the function  I'm using : &quot;def validator_for(schema, default =_UNSET):&quot; to validate through the error of my  JSON as follows:</p>
  <pre><code>from jsonschema import validate
  from jsonschema.validators import validator_for
  
  def validator_schema():
  
      sebas_schema = get_schema()
      validator = validator_for(sebas_schema)(sebas_schema)
      for error in validator.iter_errors(jsondata):
          print(error)
  
  validator = validator_schema()
  </code></pre>
  <p>This code  iterate within a JSON file against a JSON schema to validate it if one or more key or values is the same or not, So when the income JSON file doesn't have one of the keys of the expected schema, it will raise an error, but the error comes along together with the whole schema at the command line (my schema has over 1000 lines), as the following:</p>
  <pre><code>Output: 
  python3 schemas_valid.py 
  'cycle' is a required property
  
  Failed validating 'required' in schema:
      {'$schema': 'http://json-schema.org/draft-07/schema#',
       'properties': {'assessmentId': {'type': 'string'},
                      'customData': {'properties': {'missingDocuments': {'items': {'properties': {'codeGroup': {'type': 'string'},
                                                                                                  'documents': {'items': {'type': 'string'},
                                                                                                                'type': 'array'},
                                                                                                  'requires': {'type': 'number'}},
                                                                                   'required': ['codeGroup',
                                                                                                'documents',
                                                                                                'requires'],
                                                                                   'type': 'object'},
                                                                         'type': 'array'}},
                                     'required': ['missingDocuments'],
                                     'type': 'object'},
                      'cycle': {'type': 'string'},
                      'iteration': {'type': 'string'},
                      'typeCall': {'type': 'string'}},
       'required': ['typeCall',
                    'assessmentId',
                    'iteration',
                    'cycle',
                    'customData'],
       'title': 'Generated schema for Root',
       'type': 'object'}
  
  On instance:
      {'assessmentId': '123456',
       'customData': {'missingDocuments': [{'codeGroup': 'string',
                                            'documents': ['string'],
                                            'requires': 0}]},
       'iteration': '1',
       'typeCall': 'ASSESSMENT'}
  
  'cycle' is a required property
  
  Failed validating 'required' in the schema: 
  (1000 plus of JSON schema lines comes here)
  </code></pre>
  <p>Therefore, I would like to ask you guys if the output error message can be modified in the source code to only shown on the command line the first line of the error (name of the JSON key that is missing only), if so can you please guide me through where I could modify the error message in the JSON validator source code (validators.py)</p>
  <p>Any help, I would really appreciate it :).</p>