不得不 vs 只好 (forced to vs only option)

Forced or resigned?

• The last train has been cancelled and there are no taxis.
• not have / haven't没有méi yǒuwar chariot (archaic)车chē(completed / change)了le，we / us我们wǒ menhad to只好zhǐ hǎoto walk走zǒuto return回去huí qù。company公司gōng sīto stipulate规定guī dìngwant / will / need要yào(of an employee) to clock…打卡dǎ kǎ，I我wǒhad to不得不bù dé bùto get up early早起zǎo qǐ。 — "No transport left, so we'll just have to walk back. The company makes us clock in, so I have no choice but to get up early."

had to只好zhǐ hǎo = the only option left (resigned)

• had to只好zhǐ hǎo + verb = "have no choice but to", after other options have disappeared; it sounds resigned, matter-of-fact.
• the shops商店shāng diànall都dōuclosed关门guān mén(completed / change)了le，I我wǒhad to只好zhǐ hǎotomorrow明天míng tiānthen再zàibuy买mǎi.

the shops商店shāng diànall都dōuclosed关门guān mén了le，I我wǒhad to只好zhǐ hǎotomorrow明天míng tiānthen再zàibuy买mǎi。

had to不得不bù dé bù = forced (pressure, duty)

• had to不得不bù dé bù + verb = be forced to, by rules, duty or pressure: I我wǒhad to不得不bù dé bùadmit承认chéng rèn, he他tāwas ill病bìng(completed / change)了le，had to不得不bù dé bùbe hospitalised住院zhù yuàn.
• It stresses the force of the situation and is a bit more formal.

he他tāwas ill病bìng得devery很hěnseriously重zhòng，had to不得不bù dé bùbe hospitalised住院zhù yuàn。

Choosing by the force

Often interchangeable

• to rain下雨xià yǔ(completed / change)了le，we / us我们wǒ menhad to只好zhǐ hǎo / had to不得不bù dé bù待在家里dài zài jiā lǐ — both possible; had to不得不bù dé bù sounds more forced.
• had to不得不bù dé bùadmit承认chéng rèn is a fixed expression: "I have to admit".

I我wǒhave to不得不bù dé bùadmit承认chéng rènhe他tāsaid说shuō得deright对duì。

Recap

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