Connotations of なら vs たら in conditional clauses


I am wondering about the choice of, and general necessity of, なら in the
following sentence.

> ドイツでは、ウイルスがうつらないように気をつけている **なら** 、店を開くことができます。(from [NHK
> Easy](https://www3.nhk.or.jp/news/easy/k10012685971000/k10012685971000.html))
>
> * In Germany, businesses may remain open if they are careful not to spread
> the virus. (my trans.)

According to _DBJG_ , なら means roughly 'under the condition that something is
true'. How does this work in the context of the above sentence, in particular
why would たら not be appropriate, since (in my mind) any if-clause always
assumes its own validity.

Does the なら carry a sense of "actually" or "really" here? For example, would
it be more accurate to translate the sentence as " _... if the businesses are
really ensuring the virus doesn't spread_ "? Or does なら contain a sense of "
_so long as_ ", i.e. suggesting that the condition is liable to change over
time, " _...as long as the businesses are ensuring the virus doesn't spread._
"?




It's a matter of BEFORE / AFTER.

なら is like BEFORE you do Y, the precondition X must be met. I tell my kids,
おそといくなら、くつはこうね！ "Before you can go outside, you have to put shoes on!"

たら is like AFTER you do Y, you must do Z. I say to my kids, ごはんたべたら、はをみがこうね。
When you are done eating dinner, brush your teeth.

