难免 / 不免: inevitably, bound to
副词 / adverbs
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
S + 难免 + (会) + V | S + 不免 + V (reaction)
难免 means "hard to avoid": "it's only natural that", "bound to". It's often used to reassure: 犯错是难免的 (mistakes are inevitable).
不免 (adverb) describes a natural reaction to a situation: "can't help but". It often governs a feeling (不免有些担心).
难免 can also be a predicate: …是难免的. 不免 can't.
Examples
刚开始工作，犯点儿错是难免的。
Gāng kāishǐ gōngzuò, fàn diǎnr cuò shì nánmiǎn de.When you've just started a job, a few mistakes are inevitable.
第一次离开家，心里难免会有点儿孤独。
Dì-yī cì líkāi jiā, xīn lǐ nánmiǎn huì yǒudiǎnr gūdú.Leaving home for the first time, you're bound to feel a bit lonely.
听到这个消息，大家不免有些失望。
Tīngdào zhège xiāoxi, dàjiā bùmiǎn yǒuxiē shīwàng.Hearing the news, everyone couldn't help feeling a little disappointed.
Common mistakes
✗ 难免不犯错: 难免 + negation gets confusing. Prefer ✓ 难免会犯错。
✗ 这是不免的 → ✓ 这是难免的。