גם כשיש גבול ברור, לא תמיד קל לשים לב מתי עברנו אותו.

Here גם gives the sense of even:

• גם כשיש גבול ברור = even when there is a clear boundary

It adds emphasis: the speaker is saying that the problem remains true even in a situation that seems like it should be easier.

כשיש means when there is.

It is made of:

• כש־ = when
• יש = there is / there are

So:

• יש גבול = there is a boundary
• כשיש גבול = when there is a boundary

A useful point: in present-tense existential sentences, Hebrew usually uses יש, not a present-tense form of to be.

In Hebrew, adjectives usually come after the noun they describe.

So:

• גבול = boundary / limit
• ברור = clear

Together:

• גבול ברור = a clear boundary

Also, the adjective must agree with the noun in gender and number:

• גבול is masculine singular
• so the adjective is ברור (masculine singular)

Because Hebrew does not need a dummy subject like English it in sentences such as:

• It is easy
• It is hard

Hebrew simply says:

• קל = easy
• קשה = hard

So:

• לא תמיד קל לשים לב... = It is not always easy to notice...

Literally, Hebrew is closer to Not always easy to notice...

לא תמיד means not always.

That is the natural way to express partial negation:

• sometimes yes, sometimes no

By contrast, תמיד לא would sound more like always not, which is much stronger and much less natural here. If you want to say never, Hebrew usually says:

• אף פעם לא

So:

• לא תמיד קל = it is not always easy
• not = it is never easy

Because Hebrew often uses the masculine singular form as the default in impersonal expressions.

In sentences like:

• קל להבין
• קשה לדעת
• מותר להיכנס
• אסור לעשן

the adjective or predicate is usually masculine singular, even though there is no concrete masculine noun right before it.

So קל here is the normal impersonal form: easy.

לשים לב is a very common idiom meaning:

• to pay attention
• to notice

Literally, לב means heart, so the expression is historically something like to place one’s heart/attention on something. But in modern Hebrew you should just learn לשים לב as a fixed phrase.

In this sentence, the best translation is:

• to notice

So:

• קל לשים לב מתי... = easy to notice when...

Because מתי introduces an indirect question:

• מתי עברנו אותו = when did we cross it?

After verbs like know, remember, notice, Hebrew often uses question words this way:

• אני יודע מתי הוא מגיע = I know when he arrives
• שמתי לב איפה טעיתי = I noticed where I made a mistake

So here:

• לשים לב מתי עברנו אותו = to notice when we crossed it

If you used כש, it would feel more like a regular time clause, not the thing being noticed.

Because the action of crossing the boundary is viewed as a completed event.

So:

• עברנו = we crossed

In English, this may be translated either as:

• we crossed
• we have crossed

depending on context.

Hebrew often uses the simple past where English might prefer the present perfect. In this sentence, the idea is: it is not always easy to notice the moment after we have already gone past the boundary.

Yes, both verbs can relate to crossing, but they are not identical.

• לעבור = to pass, go beyond, cross
• לחצות = to cross from one side to another

In this sentence, לעבור את הגבול is especially natural and idiomatic because it can mean:

• to cross a line
• to go too far
• to overstep a boundary

So עברנו אותו works very well for a literal or metaphorical boundary.

It is most likely a generic we.

That means it does not necessarily refer to a specific group including the speaker. Hebrew, like English, often uses we in a general human sense:

• people
• any of us
• one

So the sentence means something like:

• people do not always notice when they have crossed the line

אותו refers back to גבול.

Since גבול is masculine singular, the pronoun must also be masculine singular:

• גבול → אותו

So:

• עברנו אותו = we crossed it

If the noun were feminine, Hebrew would use אותה instead.

Because אותו is already the direct-object form.

Compare:

• עברנו את הגבול = we crossed the boundary
• עברנו אותו = we crossed it

When the object is a full definite noun like הגבול, you use את.

When the object is a pronoun like אותו, you do not add another את before it.

No.

They look similar, but they mean different things:

• אותו = him / it as a direct object
• איתו = with him

So in this sentence:

• עברנו אותו = we crossed it

Not:

• we crossed with him

This is a very common confusion for learners, so it is good to notice the difference early.