Here are some examples:
* "I'll lock the door lest someone break in." This means you're locking the door to prevent someone from breaking in.
* "She finished her work quickly lest she miss her appointment." This means she worked quickly to avoid missing her appointment.
* "He spoke softly lest he wake the baby." This means he spoke softly to avoid waking the baby.
Essentially, "lest" introduces a clause that explains why the speaker is taking a particular action or expressing a particular concern.
It's worth noting that "lest" is a somewhat formal word and is less common in everyday speech.