קשה לי להאמין שהוא שכח שוב את המפתח, במיוחד כי אפילו אתמול הזכרתי לו.

This is a very common Hebrew structure.

• קשה = hard / difficult
• לי = to me / for me
• להאמין = to believe

So קשה לי להאמין literally means it is hard for me to believe, which is the natural Hebrew way to express I find it hard to believe.

Hebrew often uses this kind of pattern:

• קל לי להבין = It’s easy for me to understand
• קשה לי לזכור = It’s hard for me to remember
• נעים לי להכיר אותך = It’s pleasant for me to meet you

So the idea is not phrased as I am hard-believing, but rather it is difficult for me to believe.

The ל here is the normal prefix for the infinitive in Hebrew, similar to English to before a verb.

• להאמין = to believe
• לזכור = to remember
• לשכוח = to forget

So in קשה לי להאמין, the infinitive להאמין is just to believe.

שהוא means that he.

It is made of:

• ש־ = that
• הוא = he

So:

• קשה לי להאמין שהוא שכח = It’s hard for me to believe that he forgot

In Hebrew, ש־ is extremely common for introducing a subordinate clause:

• אני יודע שהוא כאן = I know that he is here
• חשבתי שהיא תבוא = I thought that she would come

שכח is the past tense, third person masculine singular: he forgot.

Its dictionary form is usually given as לשכוח = to forget.

A few related forms:

• שכחתי = I forgot
• שכחת = you forgot
• שכח = he forgot
• שכחה = she forgot
• שכחנו = we forgot

So שהוא שכח שוב את המפתח means that he forgot the key again.

שוב means again.

In this sentence:

• שכח שוב = forgot again

That placement is very natural in Hebrew. Hebrew word order is somewhat flexible, but verb + שוב is very common.

Compare:

• הוא שוב שכח את המפתח = He again forgot the key / He forgot the key again
• הוא שכח שוב את המפתח = He forgot the key again

Both are possible, but the version in your sentence sounds very natural.

This את is the marker of a definite direct object.

• המפתח = the key → definite
• therefore Hebrew uses את

So:

• שכח את המפתח = forgot the key

But if the object were indefinite, you would usually not use את:

• שכח מפתח = forgot a key

This את does not mean with here. It is just a grammatical marker used before definite direct objects.

More examples:

• ראיתי את הילד = I saw the boy
• קניתי את הספר = I bought the book

במיוחד means especially.

So:

• במיוחד כי... = especially because...

It adds emphasis. The speaker is saying not just It’s hard for me to believe, but It’s hard for me to believe, especially because...

It highlights the reason that makes the situation even more surprising.

Yes. כי can mean different things depending on context, most commonly that or because.

Here it means because:

• במיוחד כי אפילו אתמול הזכרתי לו = especially because I even reminded him yesterday

Examples of the two uses:

• אני חושב כי הוא צודק = I think that he is right
  (more formal/literary; everyday Hebrew often uses ש־ instead)
• אני לא בא כי אני עייף = I’m not coming because I’m tired

In your sentence, the meaning is clearly causal: it gives the reason.

אפילו means even.

Here:

• אפילו אתמול = even yesterday

The speaker means that the reminder happened as recently as yesterday, which makes the forgetting more surprising.

Placing אפילו before אתמול makes yesterday the surprising element:

• especially because I even reminded him yesterday

If you move אפילו, the emphasis can shift slightly.

Hebrew often moves time expressions earlier in the clause for emphasis or natural flow.

So:

• אפילו אתמול הזכרתי לו = I even reminded him yesterday

is very natural.

You could also say:

• אפילו הזכרתי לו אתמול

but אפילו אתמול strongly highlights yesterday.

So the word order helps emphasize how recent the reminder was.

Because the verb להזכיר often works as to remind someone of something, and the person being reminded is commonly introduced with ל־.

• הזכרתי לו = I reminded him
  literally, I reminded to him

In fuller form, Hebrew often uses:

• הזכרתי לו את המפתח = I reminded him about the key
• הזכרתי לו לקחת את המפתח = I reminded him to take the key

So in your sentence, the thing reminded is left unstated because it is obvious from context.

Using הזכרתי אותו would mean something different or sound wrong in this context. The person reminded is not treated here as a simple direct object.

Grammatically, לו means to him.

But in English, the natural translation is often simply him:

• הזכרתי לו
  literal: I reminded to him
  natural English: I reminded him

This is a very common difference between Hebrew and English. Hebrew often uses ל־ where English uses a plain object.

The word I is built into the verb form.

• הזכרתי = I reminded

The ending ־תי marks first person singular past.

So Hebrew often leaves out the separate pronoun אני unless it is needed for emphasis or contrast.

Compare:

• הזכרתי לו = I reminded him
• אני הזכרתי לו = I reminded him

The second version adds emphasis, as if contrasting with someone else.

הזכרתי comes from the root ז־כ־ר, which is connected to memory and remembering.

Some related words:

• לזכור = to remember
• זכרתי = I remembered
• הזכרתי = I reminded
• זיכרון = memory
• מזכרת = souvenir / keepsake

Notice the difference:

• לזכור = to remember
• להזכיר = to remind

That extra ה pattern changes the meaning from remembering something yourself to causing someone else to remember.

Because זכרתי means I remembered, while הזכרתי means I reminded.

That’s an important distinction:

• זכרתי את המפתח = I remembered the key
• הזכרתי לו את המפתח = I reminded him about the key

In your sentence, the speaker did not simply remember; they caused him to remember, or tried to.

Yes, it is natural and understandable.

• במיוחד = especially
• כי = because

Together:

• במיוחד כי... = especially because...

You may also see alternatives such as:

• במיוחד משום ש...
• בפרט כי...

But במיוחד כי is perfectly normal in everyday Hebrew.

Not in this exact structure.

• שכח = he forgot
• לשכוח = to forget

Since the sentence is talking about a completed event, Hebrew uses the past tense:

• שהוא שכח שוב את המפתח = that he forgot the key again

If you used לשכוח, you would need a different structure, for example:

• קשה לי להאמין שהוא מסוגל לשכוח שוב את המפתח
  = It’s hard for me to believe that he is capable of forgetting the key again

So the infinitive and the past tense are not interchangeable.

It is fairly close, but a few parts are more literal in Hebrew:

• קשה לי להאמין = hard for me to believe
• שהוא שכח שוב את המפתח = that he forgot the key again
• במיוחד כי אפילו אתמול הזכרתי לו = especially because even yesterday I reminded him

The main places where Hebrew differs from English are:

1. לי = literally to me / for me
2. לו = literally to him
3. the use of את before a definite direct object
4. pronouns like I being omitted because the verb already shows the subject

So the meaning is very straightforward, but the grammar reflects typical Hebrew patterns.

A few useful points:

• קשה = ka-SHE
• להאמין = leha’a-MIN
• שהוא = she-HU
• שכח = sha-KHACH
• המפתח = ha-maf-TE’ACH
• במיוחד = bi-myu-CHAD
• אפילו = a-FI-lu
• אתמול = et-MOL
• הזכרתי = hiz-KAR-ti
• לו = lo

A common point for learners is להאמין, because the א creates a slight break: le-ha-a-min, not a single smooth syllable like English leh-min.

Also, שכח and המפתח contain sounds that may be pronounced with the Hebrew kh sound, depending on accent.

Yes, in terms of sense, that is often a very good English rendering.

Literal:

• even yesterday

Natural interpretation:

• as recently as yesterday

That captures the speaker’s point well: the reminder happened very recently, so the forgetting is hard to believe.

It breaks down like this:

1. קשה לי להאמין
   = It’s hard for me to believe

2. שהוא שכח שוב את המפתח
   = that he forgot the key again

3. במיוחד כי אפילו אתמול הזכרתי לו
   = especially because I even reminded him yesterday

So the sentence has:

• a main expression of reaction
• a subordinate clause with ש־
• another subordinate clause introduced by כי giving the reason

This kind of layered structure is very common in natural Hebrew.