洗濕個頭 [－湿个头]

Jyutping sai2 sap1 go3 tau4
Pinyin xǐ shī gè tóu

Definitions (粵典–words.hk)
  1. 語句
    形容​某​啲​事​一開始​咗​，​就要​硬住​頭皮​繼續​做​落​去
    somthing that you cannot change or stop once it has been started
    • 𠵱家已經畀咗1萬蚊中介費，洗濕咗個頭，唔可以改變主意突然唔請個工人。
      𠵱家已经畀咗1万蚊中介费，洗湿咗个头，唔可以改变主意突然唔请个工人。
      I have already paid ten thousands agency fee to the domestic helper agency so I can't change my mind now because what's done is done.
Definitions (Wiktionary)
  1. verb, Cantonese, verb-object
    to do something that one must continue doing once it was started
Definitions (Kaifangcidian)
  1. 身不由己
  2. 欲罷不能 – 欲罢不能
  3. 已經下了水 – 已经下了水
  4. 已經陷進去了 – 已经陷进去了
  5. 沒有回頭的餘地 – 没有回头的余地

洗濕個頭 [－－个头]

Jyutping sai2 sap1 go3 tau4
Pinyin xǐ chì ge tóu

Definitions (CC-CANTO)
  1. describes a situation where a person has already started in doing something and it is not a good idea to turn back or stop half way; literally 'the head is already wet'; to be entangled in a situation that can not be withdrawn easily