"you know what they say" meaning in English

{
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        "2": "phrase"
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      "expansion": "you know what they say",
      "name": "head"
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  "lang": "English",
  "lang_code": "en",
  "pos": "phrase",
  "senses": [
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          "name": "English entries with incorrect language header",
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          "source": "w"
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      "examples": [
        {
          "ref": "2011 January 30, Sherry Jones, “Opinion: What I Saw In Egypt”, in AOL News",
          "text": "You know what they say about fish and company. After three days, you start to stink. -- but after three decades of Hosni Mubarak, the stench has become unbearable.",
          "type": "quotation"
        },
        {
          "ref": "2007, Katherine D. Bennett, Forever One",
          "text": "You know what they say about men with big feet, don't ya?\" A man in back smirked at me. I really didn't know what to say. I had heard the saying about men with big feet were supposed to be well hung, but I had no idea what would happen if I said something.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Used to introduce, or alluding to, an apt adage."
      ],
      "id": "en-you_know_what_they_say-en-phrase-xWQbVXmw",
      "links": [
        [
          "adage",
          "adage#English"
        ]
      ],
      "related": [
        {
          "word": "they say"
        },
        {
          "word": "so they say"
        },
        {
          "word": "as the saying goes"
        }
      ]
    }
  ],
  "word": "you know what they say"
}

{
  "head_templates": [
    {
      "args": {
        "1": "en",
        "2": "phrase"
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      "expansion": "you know what they say",
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  "lang": "English",
  "lang_code": "en",
  "pos": "phrase",
  "related": [
    {
      "word": "they say"
    },
    {
      "word": "so they say"
    },
    {
      "word": "as the saying goes"
    }
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      "examples": [
        {
          "ref": "2011 January 30, Sherry Jones, “Opinion: What I Saw In Egypt”, in AOL News",
          "text": "You know what they say about fish and company. After three days, you start to stink. -- but after three decades of Hosni Mubarak, the stench has become unbearable.",
          "type": "quotation"
        },
        {
          "ref": "2007, Katherine D. Bennett, Forever One",
          "text": "You know what they say about men with big feet, don't ya?\" A man in back smirked at me. I really didn't know what to say. I had heard the saying about men with big feet were supposed to be well hung, but I had no idea what would happen if I said something.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Used to introduce, or alluding to, an apt adage."
      ],
      "links": [
        [
          "adage",
          "adage#English"
        ]
      ]
    }
  ],
  "word": "you know what they say"
}