Psalm 7:15, "He has dug a hole, and has fallen into the pit which he made," is a powerful metaphor expressing the concept of poetic justice or retribution. It essentially means:

Someone who plots evil or sets traps for others will ultimately be caught in their own schemes and suffer the consequences of their own actions.

Here's a breakdown of the metaphor:

"He has dug a hole": This refers to the act of plotting evil, scheming, or setting a trap for someone else. The person is actively working to harm another.
"Has fallen into the pit which he made": This means that the very trap or harmful situation that the person created for someone else has now ensnared them. They are the victim of their own malice.

The verse illustrates a common theme in the Psalms:

God's justice ensures that evildoers will not ultimately succeed in their wickedness.
Their own wickedness will recoil upon them.

In essence, the verse is saying that evil is self-destructive. It's a warning that those who plot against others will eventually find themselves the victims of their own designs. It's a concept found in many cultures and is often summarized as "What goes around, comes around."

Examples of this principle in action (either literally or figuratively) might include:

A person who spreads rumors that ruin someone else's reputation finds themselves the target of similar malicious gossip.
A con artist who sets up a scam gets caught in a sting operation and is arrested.
A politician who corruptly undermines democratic institutions is eventually ousted and discredited.

The verse is a reminder that integrity and righteousness are ultimately the best path, as those who choose evil will ultimately be brought down by their own actions.