～次第です— The Reason Being…

• 急な用事ができ、欠席させていただく次第です。

  Kyuu na youji ga deki, kesseki sasete itadaku shidai desu.

  An urgent matter has come up, and so I will be absent — that is the situation.

  次第です formally explains the reason for the absence

• そういうわけで、お願いに参った次第です。

  Sou iu wake de, onegai ni maitta shidai desu.

  For that reason, I have come to make this request.

  参った (humble 'came') + 次第です explains why the speaker has come

• 皆様のご協力のおかげで、無事に完成した次第です。

  Minasama no gokyouryoku no okage de, buji ni kansei shita shidai desu.

  Thanks to everyone's cooperation, it has been completed without incident — such is the case.

  完成した + 次第です gives a polite account of the outcome

• ・Register: very formal; used in speeches, business emails, and apologies.
• ・Often preceded by an explanation of circumstances leading to a conclusion.
• ・Distinct from 次第 meaning 'as soon as' (連絡し次第) and 'depending on' (あなた次第).

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ～次第です is tested against.

• について — On the Subject Of
• に反して — Against Expectation
• に基づいて — Built on a Foundation
• ～上/上は/上も — In Terms Of, From the Standpoint Of
• ～に至って — Reaching the Extreme Point
• ～を契機に — Seizing the Turning Point
• ～を問わず — Regardless Of
• ～をはじめ／をはじめとして — Starting With