Question: There is a famous sentence in my language (maybe it exists in other languages too), which is

> 
> what doesn't kill you, makes you stronger
> 
> 
> 

I tried to translate exactly from my language, that is why i used **doesn't**, but i am thinking about it as an English learner. Should it be **didn't** ? because the meaning of the sentence is `what didn't kill you **in the past**,` will make you stronger **in the future**

Answer: 
The way you have it is the more natural way to say it (and indeed this expression is often said with exactly these words in English). The English simple present tense is used to describe an ongoing situation or a general truth, like this one. This is true even if the event that you are interpreting took place in the past. Example:

> 
> Cheryl: I broke my leg last year.
> 
> 
> Alice: Well, what doesn't kill you makes you stronger.
> 
> 
> Cheryl: Actually, it made me a lot weaker, because I could only walk on one leg.
> 
> 
> 

You could make it past tense if you were describing a specific event, but that would be a little weird, since the present tense version of this specific proverb is a well-known phrase:

> 
> Cheryl: I broke my leg last year.
> 
> 
> Alice: Since that didn't kill you, that must have made you stronger.
> 
> 
> Cheryl: Our friendship is over.
> 
> 
> 

Finally, you can use the past tense if the maxim is no longer relevant.

> 
> Alice: When I was young, what didn't kill me made me stronger.
> 
> 
>
Let's take another contemporary English saying or adage: 

**Karma's a bitch!**

That is, Karma *is* a bitch. Present tense. A typical context for its use is one where the villains in a movie have just received their comeuppance.

Let's make it not a very good movie. The villains are a bunch of bullies who have been stealing the lunch bags of younger kids on their way to school. One of the villains eats a stolen banana, throws the banana peel onto the sidewalk, and then slips and falls on the banana peel. Even though the action of his slipping and falling has already taken place:

Little Kid: Karma's a bitch.

The End