I was writing a conclusion and I'm in need of using an idiom with this meaning. I remember there is one (but might be confused with other language's idioms, if so pls correct me) but it seems to have zero results online. If there it none, pls suggest any other phrases/sentences on how to express this meaning.
Fire is a good friend but a bad master.
The old saying "Fire is a good friend but a bad master" is quite true.
Fire is a good servant but a bad master [proverb]
Fire is useful when monitored and controlled. Left unchecked, however, it is quite dangerous and destructive.
Oxford Reference gives the idiomatic broadening:
Fire is a good servant but a bad master
Something that is benign and useful if well controlled becomes a danger if it is allowed to take over.
And a famous example (in three variants!):
A cautionary statement about statecraft has often been attributed to George Washington. Here are three versions:
Government is like fire, a dangerous servant and a fearful master.
Government, like fire, is a troublesome servant and a terrible master.
A government is like fire, a handy servant, but a dangerous master.
And other variants:
The press, like fire, is an excellent servant, but a terrible master. [James Fenimore Cooper]
Technology is a useful servant but a dangerous master [Christian Lous Lange]