Learn Arabic (Modern Standard): إن ولاء العملاء سر نجاح هذه الشركة. - Indeed, client loyalty is the secret to the success of this company.

We are currently learning about إيّا for focalization. Since the English translation emphasizes 'Indeed', why don't we use an independent accusative pronoun here?

The particle إيّا is used to emphasize a direct object by separating it from a verb and bringing it forward. Because this is a nominal sentence with no verb and no direct object, إيّا cannot be used. The emphasis is instead provided by the particle إنّ at the beginning of the sentence.

How does إنّ affect the vowel endings of the first phrase, ولاء العملاء (client loyalty)?

The particle إنّ forces its subject into the accusative case (mansub). Therefore, ولاء takes a fatha and becomes ولاءَ. However, العملاء is the second part of an Idafa (possessive construction), so it remains unaffected by إنّ and stays in the genitive case (majrur), taking a kasra: العملاءِ.

The phrase سر نجاح هذه الشركة means 'the secret of the success of this company'. What is the grammatical case of the word سر here?

It is in the nominative case (marfu') and takes a damma, becoming سرُّ. In a sentence starting with إنّ, the subject becomes accusative, but the predicate (khabar) - which is سر in this case - remains nominative.

How do the words هذه الشركة fit into the possessive Idafa chain of سر نجاح?