one-trick pony
US /wʌn-trɪk ˈpoʊ.ni/
UK /wʌn-trɪk ˈpoʊ.ni/

1.
只會一招的馬, 只有一種技能的人
a person or thing that has only one special ability, skill, or area of expertise
:
•
He's a talented singer, but he's a bit of a one-trick pony, only performing ballads.
他是一位才華橫溢的歌手,但他有點像個只會一招的馬,只唱情歌。
•
The new software is a one-trick pony; it only does one thing well.
這款新軟體是個只會一招的馬;它只擅長做一件事。