"little did one know" meaning in English

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "little did one know (not comparable)",
      "name": "en-adv"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adv",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "Little did we know, we would be stuck in traffic for hours before finally making it back home."
        },
        {
          "ref": "2013 November 6, Stephanie Slifer, “Michelle Knight, Cleveland kidnapping survivor, details horrific circumstances inside Ariel Castro's home”, in CBS News",
          "text": "Knight said Castro told her, \"You're only going to be here as a friend, that's it. And I'll let you go on Christmas.\" Little did she know she would be held captive in his Cleveland home for more than ten years.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Used to show a relevant fact that is unknown to a person, or that the result or sequence of events differs greatly from what one had expected with the little knowledge he or she had about the situation beforehand."
      ],
      "id": "en-little_did_one_know-en-adv-QsVkqpBH",
      "related": [
        {
          "word": "next thing one knows"
        }
      ],
      "tags": [
        "not-comparable"
      ]
    }
  ],
  "word": "little did one know"
}

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "little did one know (not comparable)",
      "name": "en-adv"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adv",
  "related": [
    {
      "word": "next thing one knows"
    }
  ],
  "senses": [
    {
      "categories": [
        "English adverbs",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English terms with quotations",
        "English uncomparable adverbs"
      ],
      "examples": [
        {
          "text": "Little did we know, we would be stuck in traffic for hours before finally making it back home."
        },
        {
          "ref": "2013 November 6, Stephanie Slifer, “Michelle Knight, Cleveland kidnapping survivor, details horrific circumstances inside Ariel Castro's home”, in CBS News",
          "text": "Knight said Castro told her, \"You're only going to be here as a friend, that's it. And I'll let you go on Christmas.\" Little did she know she would be held captive in his Cleveland home for more than ten years.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Used to show a relevant fact that is unknown to a person, or that the result or sequence of events differs greatly from what one had expected with the little knowledge he or she had about the situation beforehand."
      ],
      "tags": [
        "not-comparable"
      ]
    }
  ],
  "word": "little did one know"
}