The story
From pains + taking; see take pains. The /ˈpeɪnˌsteɪkɪŋ/ pronunciation which dominates in the United States suggests a reanalysis of the word as pain + staking.
Etymology from Wiktionary, CC BY-SA 4.0.
painstaking
Today it means: Carefully attentive to details; studious; diligent in performing a process or procedure. Full definition →