In short

These are frozen evaluative predicate frames: a nominalizer (-기) or a bound noun (법, 따름, 리, 나머지, 바, 셈) sits at the end of a clause and stamps a fixed stance on it - inevitability, likelihood, futility, or “it depends.” 누구나 실수하기 마련이에요 (nuguna silsuhagi maryeonieyo, everyone is bound to make mistakes) is not “makes a mistake” plus a word; it is one set expression meaning it’s only natural to. Learn each as a chunk, and learn its register - some are everyday 해요체, others belong to editorials and speeches.

The rule

Step 1 - The shared machinery, and the two spacing families

Every pattern here is clause + connector + 이다 (or 없다, or 치다 in 셈 치고). The connector is either the nominalizer -기 (glued to the stem, then a space) or a bound noun after a modifier ending (-(으)ㄴ / -는 / -(으)ㄹ, then a space). The tail carries the sentence: copula 이다 -> 해요체 -이에요 after a consonant, -예요 after a vowel (마련이에요, 법이에요, 십상이에요 but 일쑤예요), or 없다 -> 없어요 - and because the tail is the copula, it is also where tense goes: 일쑤였어요 (ilssuyeosseoyo), 따름이었어요 (ttareumieosseoyo), 마련이었어요 (maryeonieosseoyo). Because these are set idioms, the register is baked in - keep spoken frames out of formal prose and editorial frames out of casual chat.

Step 2 - Inevitability and natural law: -기 마련이다, -는 법이다

Stem + -기 마련이다 (= -게 마련이다, fully interchangeable) says an outcome is only natural, bound to happen: 누구나 실수하기 마련이에요 = 누구나 실수하게 마련이에요 (nuguna silsuhage maryeonieyo). -는 법이다 (“법”, law, the way of things) is close but more sententious, the tone of a maxim: verbs take -는, adjectives -(으)ㄴ. 노력하면 성공하는 법이에요 (noryeokhamyeon seonggonghaneun beobieyo, work hard and you succeed - that’s how it goes). Both are natural in speech and in writing.

Step 3 - Likelihood and bad habit (negative only): -기 십상이다, -기 일쑤이다

Both attach to -기 and both are reserved for undesirable outcomes. -기 십상이다 = all too likely to (end badly): 급하게 먹으면 체하기 십상이에요 (geuphage meogeumyeon chehagi sipsangieyo, eat in a hurry and you’re all too likely to get indigestion). -기 일쑤이다 = does the bad thing habitually, a narrative/written flavour: 지각하기 일쑤예요 (jigakhagi ilssuyeyo, is forever turning up late). Never use either for a welcome result - that is 마련이다’s job.

Step 4 - Limitation and impossibility: -(으)ㄹ 따름이다, -(으)ㄹ 리가 없다

-(으)ㄹ 따름이다 (“따름”, bound noun) = nothing but / can only, a formal, self-effacing register: 그저 감사할 따름이에요 (geujeo gamsahal ttareumieyo, I’m nothing but grateful). -(으)ㄹ 리가 없다 (“리”, reason) denies a possibility outright - there’s no way that: 그 사람이 거짓말을 할 리가 없어요 (geu sarami geojinmareul hal riga eopseoyo). Both lock to the prospective -(으)ㄹ and take a space - a lock against -는, not against the past: a completed event takes -았/었을, as in 어제 그 소식을 못 들었을 리가 없어요 (eoje geu sosigeul mot deureosseul riga eopseoyo, there’s no way they didn’t hear the news yesterday).

Step 5 - Excess-cause and the lesser evil: -(으)ㄴ 나머지, -(으)ㄹ 바에는

-(으)ㄴ 나머지 (“나머지”, remainder) marks an extreme cause spilling into a (usually bad) result - so much X that …. It names a cause already realized, so it takes the completed -(으)ㄴ: 너무 긴장한 나머지 이름을 잊어버렸어요 (neomu ginjanghan nameoji ireumeul ijeobeoryeosseoyo, I was so nervous I forgot my own name); editorial in tone. -(으)ㄹ 바에는 (also -(으)ㄹ 바에야) = rather than (this bad option), and pairs with 차라리 (charari, rather): 포기할 바에는 차라리 끝까지 해 볼래요 (pogihal baeneun charari kkeutkkaji hae bollaeyo, rather than give up, I’d sooner see it through).

Step 6 - Opportunistic and hypothetical connectives: -는 김에, -는 셈 치고

These join clauses rather than end them. -는 김에 (verb only; past -(으)ㄴ 김에) = while you’re already at it: 나가는 김에 우유 좀 사다 주세요 (naganeun gime uyu jom sada juseyo). -는 셈 치고 = supposing / as if, treat a fiction as true and act on it: 속는 셈 치고 한번 믿어 볼게요 (songneun sem chigo hanbeon mideo bolgeyo, I’ll trust you this once, as if letting myself be fooled).

Step 7 - Contingency and framing: -기 나름이다, -는 데(에) 있어서

-기 나름이다 (also N 나름이다) = it all depends on how: 모든 일은 마음먹기 나름이에요 (modeun ireun maeummeokgi nareumieyo, everything depends on how you set your mind to it). -는 데(에) 있어서 = when it comes to / in doing, a formal calque for essays and speeches: 외국어를 배우는 데 있어서 꾸준함이 제일 중요해요 (oegugeoreul baeuneun de isseoseo kkujunhami jeil jungyohaeyo). In casual 해요체 Koreans just drop it (배울 때 / 배우려면).

Step 8 - 사자성어 and 속담: when they land, when they clang

사자성어 (sajaseongeo, four-character Sino-Korean idioms like 고진감래, gojingamnae, bitter first, sweet later) read as erudite: they land in essays, editorials, toasts and formal speeches, usually flagged with …(이)라는 말이 있듯이 (as the saying goes). Stacking several into casual chat sounds like showing off. 속담 (sokdam, native proverbs like 티끌 모아 태산, tikkeul moa taesan, dust piled up makes a mountain) are the folksy counterpart - warm in conversation, flagged with 옛말에 …(이)라고 하잖아요 - but preachy if overused. Rule of thumb: one, placed well, at the right register.

Forms & patterns

Attachment shape, spacing, and a model sentence for each frame:

Two spacing families - the single test that keeps them straight:

사자성어 vs 속담 - erudite vs folksy:

Examples

Common mistakes

• 실수하는 마련이에요 (silsuhaneun maryeonieyo) -> 실수하기 마련이에요 (silsuhagi maryeonieyo) - 마련이다 sits on the nominalizer -기, never on the modifier -는. You’re bound to make mistakes.
• 너무 긴장하는 나머지 이름을 잊어버렸어요 (neomu ginjanghaneun nameoji…) -> 너무 긴장한 나머지 이름을 잊어버렸어요 (neomu ginjanghan nameoji…) - 나머지 names a cause already realized, so it takes the completed -(으)ㄴ, not -는. I was so nervous I forgot my name.
• 그저 감사할따름이에요 (geujeo gamsahalttareumieyo) -> 그저 감사할 따름이에요 (geujeo gamsahal ttareumieyo) - 따름 is a bound noun, so a space follows the -(으)ㄹ form (same for 리, 셈, 나머지). I’m nothing but grateful.
• 그 사람이 거짓말을 하는 리가 없어요 (… haneun riga eopseoyo) -> 그 사람이 거짓말을 할 리가 없어요 (… hal riga eopseoyo) - 리 locks to the prospective -(으)ㄹ, never -는. There’s no way that person would lie.
• 열심히 하면 성공하기 십상이에요 (yeolsimhi hamyeon seonggonghagi sipsangieyo) -> 열심히 하면 성공하기 마련이에요 (yeolsimhi hamyeon seonggonghagi maryeonieyo) - 십상이다 and 일쑤이다 are for undesirable results only; a welcome, natural outcome takes 마련이다. Work hard and you’re bound to succeed.

Tips

• Spacing follows the family. If the frame is built on -기 (마련, 십상, 일쑤, 나름), glue -기 to the stem and space before the idiom. If it is built on a bound noun (법, 따름, 리, 나머지, 바, 셈, 데), first choose the modifier ending by word class and tense, then space. Get the family right and the spacing is automatic.
• The negative-outcome pair. 십상이다 (likely) and 일쑤이다 (habitual) only describe things going wrong; 마련이다 / 법이다 are neutral “that’s how it is.” Swapping them in reverses the meaning a native ear expects.
• -는 데 있어서 is a formal false friend. It calques English “in doing / when it comes to,” so it fits speeches and essays but sounds stiff in chat - there, Koreans simply say 배울 때 or 배우려면. Do not sprinkle it into 해요체 conversation.
• Idiom dosage. A single well-placed 사자성어 (고진감래) dignifies a toast; a string of them in small talk reads as pretentious. 속담 (티끌 모아 태산) is the warm, folksy alternative - homely in speech, but preachy if you lean on it.