彼此 vs 对方 (nhau so với bên kia/người đối diện)

The other side's reply is a one-sided event

• You call someone, and the person at the other end speaks first.
• telephone电话diàn huàto connect接通jiē tōngback后hòu，the other person对方duì fāng先开xiān kāi(completed / change)了lemouth口kǒu。 — the other person对方duì fāng identifies the counterpart, not both sides together.

Locate the pattern in real examples

• each other彼此bǐ cǐ vs the other person对方duì fāng (each other vs the other party): old friend老朋友lǎo péng yǒu(after a noun) between之间zhī jiānshould应该yīng gāi___trust信任xìn rèn。; we我们wǒ men___to understand了解liǎo jiě，need not不用bù yòngmany多duōvariant of 说说shuō。
• Read the whole clause before choosing a translation. The examples show the pattern in use; the context below determines what the speaker claims.

Follow the speaker

we我们wǒ meneach other彼此bǐ cǐtrust信任xìn rèn。

• In the opening situation: telephone电话diàn huàto connect接通jiē tōngback后hòu，the other person对方duì fāng先开xiān kāi(completed / change)了lemouth口kǒu。
• the other person对方duì fāng identifies the counterpart, not both sides together.

Check the limit of the explanation

• each other彼此bǐ cǐtrust信任xìn rèn describes mutual trust; the other person对方duì fāngtrust信任xìn rènI / me我wǒ describes the other person's trust in me without asserting that I trust them.
• Track who acts on whom.

Repair the form before interpreting it

• The form we我们wǒ menthis此cǐthat彼bǐtrust信任xìn rèn needs repair here. Write we我们wǒ meneach other彼此bǐ cǐtrust信任xìn rèn instead; keep the word or frame in its demonstrated order.
• Form and meaning are separate checks. After the repair, explain the sentence in its situation rather than treating a familiar translation as a universal rule.

Keep the distinction

Read the full reference: HSK 6 grammar — Comparing similar nouns.