先入為主 [－－为－]

Jyutping sin1 jap6 wai4 zyu2
Pinyin xiān rù wéi zhǔ

Definitions (CC-CEDICT)
  1. the first impression is the strongest
  2. to hold a preconceived notion (about sth)
Definitions (粵典–words.hk)
  1. 動詞
    單單​根據​第一印象​而​判斷​，​抱持​偏見
    to judge merely according to first impressions; to have prejudice
Definitions (Wiktionary)
  1. phrase, idiomatic
    to be prejudiced by a first impression; to have a preconception