A hand-saw is a good thing, but not to shave with.

Understand the thought

Meaning in plain English

A tool can be good at its intended job and unsuitable for another. Choose according to the task rather than assuming general quality makes every use appropriate.

What the words are saying

The hand-saw is granted value before its use for shaving is rejected. That structure matters: the proverb does not condemn the tool, but the attempted application. Figuratively, a method, skill or arrangement can be excellent in one setting and poorly suited to a different one. An impressive solution should still be evaluated against the actual requirements. Rather than arguing over whether the method is good in the abstract, ask what it can do here and where its limits lie. The image is a deliberately unsuitable pairing, not an instruction to experiment with a dangerous physical use.

Everyday example

A detailed scholarly index remains useful for research, but a librarian creates a simpler introduction when visitors need help choosing their first book.

When to use it

Use it when the quality of a tool is being used to justify an application it does not suit.

Agent-assisted editorial interpretation. This explains the words; it does not by itself verify their author or earliest origin.