Learn Hardcore Japanese: zyunbi wo sinai to, sippaisimasu. - If you don’t prepare, you will fail.

準備 is a verbal noun (a noun that can pair with する “do”). In the pattern Noun + を + する, を marks the noun as the direct object of する: 準備をする = “do preparation.”
With many such nouns, you can also drop を and attach する directly: 準備する. Both are natural.
In this sentence, both 準備をしないと and 準備しないと are fine. Using を can feel a touch more formal or explicit, but the nuance difference is minimal.

What does と mean in しないと here?

It’s the conditional linking particle meaning “if/when.” So 準備をしないと、失敗します means “If you don’t prepare, you’ll fail.” The と-conditional often conveys a natural or predictable consequence.

I’ve seen しないと used to mean “I have to ….” Which meaning is it here, and how can I tell?

Standalone X しないと is shorthand for “I have to do X,” omitting the rest (e.g., 〜しないといけない/ダメ).
- Example: 準備しないと。 = “I’ve gotta prepare.”
In your sentence, しないと is followed by a result clause (失敗します), so it’s the conditional “if you don’t …, [then] ….” No obligation meaning is intended.

Why is the first clause plain (しない) but the second clause polite (失敗します)? Isn’t that mixing styles?

This is normal. Subordinate clauses (like conditionals before と) are typically in plain form, while politeness is expressed in the main clause. So 準備をしないと、失敗します is standard and natural. If you make both plain, you get 準備しないと、失敗する (casual).

Why does 失敗します (non-past) refer to the future (“will fail”)?

Japanese doesn’t have a dedicated future tense. The non-past form covers both present/habitual and future. Context (and sometimes adverbs like きっと, たぶん) shows the intended time. Here it’s a general or future consequence.

Can I replace と with other “if” forms like 〜なければ, 〜たら, 〜ば, or 〜なら? What changes?

準備をしなければ、失敗します。 Near-synonym of しないと; a bit more formal or “requirement” flavored.
準備をしなかったら、失敗します。 More event-specific/hypothetical (“if in that case you didn’t prepare, then you’ll fail”).
準備をすれば、失敗しません。 Positive framing (“If you prepare, you won’t fail”).
準備をしないなら、失敗します。 “If it’s the case that you’re not going to prepare, then you’ll fail.” Feels more like responding to a stated plan; less like a general rule.
Note: 準備をしなければならない means “must prepare,” which is a different meaning entirely.

When is the と-conditional appropriate or not?

Good for habitual truths, instructions, and natural consequences: warnings, rules, cause-and-effect.
Generally avoid と when the main clause expresses your will, a request, or a suggestion (e.g., 〜ましょう／〜てください／〜たい). Use たら／ば／なら in those cases.

Can I say 準備しないで、失敗します instead? What’s the difference between ないで and ないと?

〜ないで means “without doing …, …” and links two actions directly. It works best when you specify the action that follows:
- Natural: 準備しないで受けると、失敗します。 (“If you take it without preparing, you’ll fail.”)
- Natural: 準備しないでいると、失敗します。 (“If you stay unprepared, you’ll fail.”)
〜ないと is the conditional “if you don’t …, [then] …,” which is perfect for general warnings like your sentence.
Bare 準備しないで、失敗します sounds incomplete because the second action isn’t clearly defined.

Who is the subject here? Is it “you”?

Japanese often omits the subject when it’s obvious or generic. This sentence can mean “you,” “we,” or “people in general.” In context, it reads like a general warning/advice to the listener: “If you don’t prepare, you’ll fail.”

Why doesn’t 失敗します take an object? Is 失敗する transitive?

失敗する is intransitive (“to fail; to make a mistake”), so it doesn’t take a direct object. To specify what you failed at, use:

N に失敗する (target): 試験に失敗する (“fail an exam”).
N で失敗する (context/occasion): 面接で失敗する (“mess up at the interview”). Also, “a plan fails” is often 計画が失敗する (the plan itself fails).

Is there any nuance difference between 準備 and 用意?

準備: broader “preparation” (planning, organizing, getting ready overall).
- Examples: 発表の準備, 旅行の準備, 試験の準備
用意: more about “arrangements/readying concrete items.”
- Examples: 資料の用意, お茶の用意, お金の用意 They overlap a lot; in many cases either is acceptable.

Is the comma necessary? And what about the spaces between words?

The comma after と is optional; it just improves readability: 準備をしないと失敗します is fine.
Standard Japanese writing doesn’t use spaces between words. The spaces in your prompt are for teaching segmentation.

How would I say this more casually or more strongly?

Casual: 準備しないと失敗するよ。
Very casual/contracted: 準備しなきゃ失敗するよ。 (from しなければ)
Strong warning: 準備しないとダメだよ。 / 準備しないとまずいよ。
Formal/written: 準備をしなければ、失敗します。