"You have to forget it!"
Translation:Il faut laisser tomber !
Ok, here's my attempt at explaining the two ways you can translate this.
Literally - tu dois l'oublier (or vous devez l'oublier)
Idiomatically - tu dois laisser tomber (or vous devez laisser tomber)
Why does the idiomatic version not have an 'it'? Because as an expression it is focusing more on the attitude of 'letting fall' rather than the particular thing being forgotten. It is perhaps something like us telling someone that they have to 'smile and carry on'.
Hope this helps.
Here's a good discussion: http://forum.wordreference.com/showthread.php?t=90509
Someone brings up a good translation: "Just drop it!"
Here's a song written by Serge Gainsbourg. "Laisse tomber les filles" = "Leave the girls alone".
Then there's the following:
- J'ai laissé tombé ma copine = I broke up with my girlfriend
- J'ai laissé tombé le verre = I dropped the glass
I got this as "translate from English to French by selecting words", and couldn't figure it out because it was "You have to forget it!", but there was no oublier available. I'd just like to point out that we have the same metaphorical idiom in English: "You have to let it drop."