"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"
        },
        {
          "kind": "other",
          "name": "Entries with translation boxes",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Terms with Portuguese translations",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "I was speaking ill of Fred; little did I know that he was right behind me, listening in.",
          "type": "example"
        },
        {
          "text": "Little did we know, we would be stuck in traffic for hours before finally making it back home.",
          "type": "example"
        },
        {
          "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": "quote"
        },
        {
          "ref": "2012 May 13, Alistair Magowan, “Sunderland 0-1 Man Utd”, in BBC Sport:",
          "text": "But as United saw the game out, little did they know that, having looked likely to win their 13th Premier League title, it was City who turned the table to snatch glory from their arch-rivals’ grasp.",
          "type": "quote"
        }
      ],
      "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"
      ],
      "translations": [
        {
          "code": "pt",
          "lang": "Portuguese",
          "sense": "Translations",
          "word": "mal saber"
        }
      ]
    }
  ],
  "sounds": [
    {
      "audio": "LL-Q1860 (eng)-Flame, not lame-little did one know.wav",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/1/10/LL-Q1860_%28eng%29-Flame%2C_not_lame-little_did_one_know.wav/LL-Q1860_%28eng%29-Flame%2C_not_lame-little_did_one_know.wav.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/1/10/LL-Q1860_%28eng%29-Flame%2C_not_lame-little_did_one_know.wav/LL-Q1860_%28eng%29-Flame%2C_not_lame-little_did_one_know.wav.ogg"
    }
  ],
  "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 terms with usage examples",
        "English uncomparable adverbs",
        "Entries with translation boxes",
        "Pages with 1 entry",
        "Pages with entries",
        "Terms with Portuguese translations",
        "Translation table header lacks gloss"
      ],
      "examples": [
        {
          "text": "I was speaking ill of Fred; little did I know that he was right behind me, listening in.",
          "type": "example"
        },
        {
          "text": "Little did we know, we would be stuck in traffic for hours before finally making it back home.",
          "type": "example"
        },
        {
          "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": "quote"
        },
        {
          "ref": "2012 May 13, Alistair Magowan, “Sunderland 0-1 Man Utd”, in BBC Sport:",
          "text": "But as United saw the game out, little did they know that, having looked likely to win their 13th Premier League title, it was City who turned the table to snatch glory from their arch-rivals’ grasp.",
          "type": "quote"
        }
      ],
      "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"
      ]
    }
  ],
  "sounds": [
    {
      "audio": "LL-Q1860 (eng)-Flame, not lame-little did one know.wav",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/1/10/LL-Q1860_%28eng%29-Flame%2C_not_lame-little_did_one_know.wav/LL-Q1860_%28eng%29-Flame%2C_not_lame-little_did_one_know.wav.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/1/10/LL-Q1860_%28eng%29-Flame%2C_not_lame-little_did_one_know.wav/LL-Q1860_%28eng%29-Flame%2C_not_lame-little_did_one_know.wav.ogg"
    }
  ],
  "translations": [
    {
      "code": "pt",
      "lang": "Portuguese",
      "sense": "Translations",
      "word": "mal saber"
    }
  ],
  "word": "little did one know"
}