«طَبَّاخِ السِّم لَا بُدِّ يْدُوقُهْ»

The image is someone preparing poison who still cannot avoid a taste, whether from curiosity, a careless slip, or a smear left on a fingertip. The implied reasoning runs further: if even a poison-maker samples the brew, someone cooking something delicious will surely help himself. Applied this way, it excuses or expects small pilfering by people entrusted with others' goods.

The saying also works as a warning to anyone who sets out to injure or ensnare others. Whoever devises mischief will sooner or later be caught by some of its spatter, because no one can handle harm for long without being touched by it. In this sense it resembles the idea that a plotter falls into his own trap.

Use it when commenting on someone entrusted with food, money, or goods who is suspected of taking some for themselves, or when warning that a harmful plot may rebound on its maker. The first application implies a particular misuse of trust, not that everyone handling others’ property steals.