When you start really swimming in a language, you start noticing that there are soooooooooooo many similar words.

Only, books don't help you in distinguishing their nuance.

So you end up just blindly mixing and matching words and sentences.

In other words--you don't speak like a native speaker.

*sigh*

Four such words for me are:
1) 完璧 　　　 (kanpeki; "perfection; perfect; flawless")
2) パーフェクト 　(paafekuto; "perfect")
3) バッチリ 　　 (bacchiri; "excellent; perfect; spot-on")
4) ちょうどいい 　(choudo ii; "just right")

Here's the simple version:
完璧 (kanpeki) and パーフェクト (paafekuto) pretty much do mean "perfect" in the same (very good) sense of the English word.

バッチリ (bacchiri) pretty much means "perfect," too, although maybe it's ever so slightly less "perfect" than 完璧 (kanpeki) and パーフェクト (paafekuto).

ちょうどいい (choudo ii), sometimes written in kanji as 丁度いい does NOT mean "perfect" in any way... and even though it kind of does mean "just right," it's not really as positive as the English, "just right."

Here's a chart:

Feel free to go all out with 完璧, パーフェクト, and バッチリ...

These are really positive words, so feel free to use them when complimenting people and whatnot.

Not to brag, but here are some emails I've gotten from business contacts/clients in the past...

(Note: To maintain work confidentiality, for a lot of these, I've replaced job names as XX.)

XX 拝受いたしました。
すばらしいですね、完璧です、ありがとうございます。
XX haiju itashimashita.
subarashii desu ne, kanpeki desu, arigatou gozaimasu.
I received XX from you.
It's excellent. Just perfect. Thank you very much.

(Literally, Line #1: "XX + receiving + did")
(Literally, Line #2: "excellent + is + ね, + perfect + is, + thank you.")
(Note: This was an email from a client, and that's why he's begin soooo polite [humble form in the first line, ～いたしました instead of ～しました or ～した].)

しかしNikoの XX の勉強法？を聞いてると、
本当に完璧に近づいていくだろうね。
偉いよ。
shikashi Niko no XX no benkyouhou? wo kiiteru to,
hontou ni kanpeki ni chikadzuite iku darou ne.
erai yo.
However, hearing about the way you study XX,
I imagine you really will get close to perfect.
Very impressive.

(Literally, Line #1: "however + Niko + の + XX + の + study method? + を + hearing + と")
(Literally, Line #2: "truly + perfect + に + become close + go + probably + ね.")
(Literally, Line #3: "admirable + よ.")
(Note: This might be kind of hard to understand out of context. I had explained to my editor how I was studying a certain type of text for a writing job we were doing in which I had to mimic a certain writing style. Also, here's 偉い in action! We saw that in a previous lesson. ^_^)

XX のほうもバッチリだよ。
XX no hou mo bacchiri da yo.
XX is perfect, too.

(Literally: "XX + の + direction + also + excellent + is + よ.")
(Note: He's saying XX is perfect in addition to something else I sent him.)

代案をありがとう！
大丈夫だよ、これで。バッチリ^^
daian wo arigatou!
daijoubu da yo, kore de. bacchiri ^^
Thanks for the alternate suggestions.
This is good now. Perfect. ^^

(Literally, Line #1: "alternate + を + thank you.")
(Literally, Line #2: "OK + is + よ, + this + で. + perfect.")
(Note: He's talking about alternate samples I made for a writing job.)

Now let's compare those with the emails I've gotten that include ちょうどいい...

本当にちょうどいい感じになってきたね。
hontou ni choudo ii kanji ni natte kita ne.
It has started to really feel spot on.

(Literally: "truly + just right + feeling + become + came + ね.")
(Note: He's referring to a writing sample that we went back and forth editing several times, slowly approaching the writing style/quality that was appropriatefor the job.)

ざっと見た感じだけど、訳の量もコメントの量もちょうどいいと思うよ。
zatto mita kanji da kedo, yaku no ryou mo komento no ryou mo choudo ii to omou yo.
I just glanced over it, but I think the amount of translations and comments is just right.

(Literally: "glanced over [=ざっと見た] + feeling + but + translation + の + amount + also + comment + の + amount + also + just right + I think + よ.")
(Note: Again, for some writing/translation materials I submitted.)

Confession: I don't really understand why ちょうどいい is not as positive as 完璧, バッチリ, etc. To me, "perfect" and "just right" don't feel all that different, you know? However...

Rei was telling me that she thinks sometimes ちょうどいい can actually sound kind of rude.

For example...

あの人くらいの体型がちょうどいいよね。
ano hito kurai no taikei ga choudo ii yo ne.
Her body is just right for me.

(Literally: "that + person + の + figure + が + just right + よね")
(Note: Translating this sentence is melting my brain... because this is not really a nice thing to say about a girl's body. Rei's explanation was, "There's no way this speaker is talking about a super-beautiful model; he's just talking about a level of physical beauty adequate for him..." So yeah, not the nicest thing to say.)

We can compare that with the much more flattering...

あの人スタイル超いいよね。
ano hito sutairu chou ii you ne.
She has an amazing figure.

(Literally: "that + person + figure + super good + よね")
(Note: Notice that this usage of スタイル is Japanese-English--it means physical "figure" in Japanese, not "style" how it's used in English... although スタイル and "style" might match up in other sentences/uses. 💀 Also, since it's mad casual, we killed off all of the particles with extreme prejudice [no の after 人 // no が after スタイル].)

In Short:
Thanks to Rei, I'm now kind of afraid to use ちょうどいい for fear that I may mis-nuance it to oblivion.

Yay. \(T_T)/