Someone familiar with a certain field or behavior understands its ways — it takes one to know one.
彼がその手口を見抜いたのは当然だ。蛇の道は蛇だからね。
It's natural he saw through that trick — it takes one to know one.
プロの泥棒同士だと、片方が相手の行動をよく知っている。まさに蛇の道は蛇だ。
With professionals like thieves, one knows the other's moves well — truly, it takes one to know one.
業界のことは同業者にしか分からない部分が多い。蛇の道は蛇ということだ。
Much about the industry is only understood by insiders — it really does take one to know one.