不比不知道，一比嚇一跳 [－－－－－－－－吓－－]

Jyutping bat1 bei2 bat1 zi1 dou6 ， jat1 bei2 haak3 jat1 tiu3
Pinyin bù bǐ bù zhī dào ， yī bǐ xià yī tiào

Definitions (Wiktionary)
  1. phrase, idiomatic
    Without comparisons one is ignorant, but once one does, one gets a shock.