for nothing is ever so mischievous in its own place as it is out of it

[booklover]

It's from 'Golden Key' by George MacDonald, which I encountered today,
from below paragraph.

<Now, although she did not know it, this was the very best way she could have gone; for nothing is ever so mischievous in its own place as it is out of it; and, besides, these mischievous creatures were only the children of Fairyland, as it were, and there are many other beings there as well;and if a wanderer gets in among them, the good ones will always help him more than the evil ones will be able to hurt him.>

The above phrase is also used as a quotable quote, which I've noticed on internet.
However, I really don't understand the meaning clearly.

Any advice shall be highly appreciated.​

 

[Tarheel]

Maybe the writer means those creatures are more likely to cause trouble when they're away from home than they are in their natural environment.

 

[Charlie Bernstein]

Yes, that's what MacDonald means.