The absent are always at fault.

The saying points to an unfair habit rather than establishing that absence proves fault. A group may find it convenient to agree that someone outside the room caused a problem, especially when doing so avoids examining its own decisions. The missing person has no opportunity to supply context or correct a mistaken detail. Always is an exaggerated description of that tendency. A useful response is to distinguish known evidence from assumptions and seek the relevant account before assigning responsibility. This does not prevent identifying a genuine mistake; it asks for a fair process instead of a convenient scapegoat.

When to use it

Use it to question convenient blame directed at someone who cannot respond.

Keep in mind

Absence does not prove either guilt or innocence; the eventual judgement should rest on relevant evidence.