You're better off not knowing.
4 seconds sound clip from the Taken (2008) movie soundboard.
You can hear this line at 00:45:26 in the Blu-ray version of the movie.
Quote context
[...]
- The other one is suggesting something his grandmother used to give him for that
- Do you really want to hear all this?
- Perhaps if I knew the purpose...
- You're better off not knowing.
- He has to do a job at the construction site.
- Something about fresh merchandise giving problems.
- Mr. Smith, I do not understand any of this.
[...]