不得不 מול 只好 (נאלץ מול אופציה יחידה)

Pressure and a last resort can overlap

• The last bus has left, leaving walking as the available way home.
• last bus or train末班车mò bān chēto walk走zǒu(completed / change)了le，I我wǒto have no other option but…只好zhǐ hǎoto walk走zǒuto return home回家huí jiā。 — to have no other option but…只好zhǐ hǎo highlights accepting the remaining option.

Locate the pattern in real examples

• have to不得不bù dé bù vs to have no other option but…只好zhǐ hǎo (forced to vs only option): due to由于yóu yútyphoon台风tái fēng，(scheduled) flight航班háng bān___to cancel取消qǔ xiāo。; doctor医生yī shēngvariant of 说说shuōto have to必须bì xūrest休息xiū xī，he / him他tā___to lay down放下fàng xiàto work工作gōng zuò。
• 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

I我wǒhave to不得不bù dé bùagree同意tóng yì。

• In the opening situation: last bus or train末班车mò bān chēto walk走zǒu(completed / change)了le，I我wǒto have no other option but…只好zhǐ hǎoto walk走zǒuto return home回家huí jiā。
• to have no other option but…只好zhǐ hǎo highlights accepting the remaining option.

Check the limit of the explanation

• I我wǒhave to不得不bù dé bùto walk走zǒuto return home回家huí jiā also fits this situation, stressing necessity.
• Do not label one option impossible just because the other emphasises resignation more clearly.

Repair the form before interpreting it

• The form I我wǒgood好hǎoonly只zhǐto walk走zǒuto return home回家huí jiā needs repair here. Write I我wǒto have no other option but…只好zhǐ hǎoto walk走zǒuto return home回家huí jiā 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 adverbs.