The empty leech sucks sore.

A hungry leech fastens on and feeds more painfully, because urgent need makes its taking more forceful and relentless.

The saying warns that severe want may make someone press demands harder and harm the person treated as a resource; it should not be read as claiming that people in poverty or dependence are inherently exploitative.

Use it as a caution that urgent need can make reliance feel relentlessly extractive, whether literally of a blood-feeding leech or figuratively of a dependency. The comparison can sound harsh, especially when aimed at people experiencing poverty or dependence.