Мне ужасно не хотелось выходить под дождь, но я всё-таки пошла за книгой.

Because не хотелось uses an impersonal construction.

Мне не хотелось... literally means something like To me, it was not wanted... or more naturally I didn’t feel like...

So:

• я не хотела = I didn’t want to
• мне не хотелось = I didn’t feel like / I really didn’t want to

The second version sounds more about inner reluctance or lack of desire, rather than a direct, firm intention.

This is an important nuance.

• я не хотела выходить = I didn’t want to go out
• мне не хотелось выходить = I didn’t feel like going out

Не хотела is more straightforward and personal: the speaker consciously did not want to do it.

Не хотелось is softer and more emotional. It often suggests:

• lack of inclination
• reluctance
• discomfort
• I really wasn’t in the mood to...

In this sentence, мне ужасно не хотелось sounds very natural because the speaker is describing a strong feeling of reluctance.

Because хотелось here is part of an impersonal construction.

In impersonal expressions, Russian often uses a neuter singular past form:

• мне хотелось
• мне не спалось
• мне повезло

These do not agree with the gender of the person experiencing the feeling.

By contrast, пошла is a normal past-tense verb with an actual subject я, so it must agree with the speaker’s gender:

• пошёл = masculine
• пошла = feminine

Here ужасно means terribly, awfully, or really.

It intensifies the feeling:

• мне не хотелось = I didn’t feel like it
• мне ужасно не хотелось = I really / terribly didn’t feel like it

It does not literally mean something horrifying is happening. In everyday Russian, ужасно is often just a strong adverb of degree.

Because after хотелось / не хотелось, Russian often uses the infinitive to describe the action in a general way, and here выходить presents the action as the act of going out, without focusing on completion.

• выходить = imperfective
• выйти = perfective

In this sentence, выходить под дождь means to go out into the rain, focusing on the unpleasant idea of doing that action.

You could encounter не хотелось выйти in some contexts, but не хотелось выходить is very natural when talking about reluctance toward the action itself.

This is a very common learner question.

• под дождь = into the rain
• под дождём = under the rain / in the rain

Here, выходить под дождь means to go out into the rain, emphasizing movement into that condition.

Russian often uses:

• идти под дождём = to walk in the rain
• выйти под дождь = to step out into the rain

So the accusative after под here shows direction or movement.

Всё-таки means all the same, nevertheless, still, or after all.

It shows that something happened despite resistance, doubt, or obstacles.

So:

• но я всё-таки пошла = but I went anyway / but I still went

It highlights the contrast:

• I really didn’t want to go out in the rain,
• but I did it anyway.

Пошла is the past tense of пойти, which often means set off / started going / went.

Here it fits well because the speaker decided to go somewhere despite not wanting to.

• пошла = went / set off
• шла = was walking / went on foot with emphasis on the process
• ушла = left / went away

So я всё-таки пошла за книгой means I ended up going for the book or I set off to get the book.

Because за can mean for / to get, and in that meaning it takes the instrumental case.

So:

• пойти за книгой = to go get a book / to go for the book
• сходить за хлебом = to go get bread
• послать за врачом = to send for a doctor

Here книгой is instrumental singular of книга.

This use of за + instrumental often means going somewhere in order to fetch or pick something up.

In this sentence, it is most naturally understood as for the book or to get a book, depending on context.

Russian has no articles, so книгой alone does not tell you whether it is:

• a book
• the book
• my book
• that book

You understand that from context.

So пошла за книгой could mean:

• went to get the book
• went to get a book

If the broader context is known, one interpretation will be more likely.

In the first half, я is not needed because the construction is impersonal:

• Мне ужасно не хотелось...

The experiencer is already clear from мне.

In the second half, Russian includes я because now there is a normal personal verb:

• но я всё-таки пошла

It is possible to omit я there too in some contexts, but keeping it makes the contrast clearer and more natural:

• I really didn’t want to..., but I went anyway.

The sentence has very natural word order, but Russian word order is flexible.

This version:

• Мне ужасно не хотелось выходить под дождь, но я всё-таки пошла за книгой.

sounds neutral and smooth.

The order helps the sentence flow like this:

1. experiencer: мне
2. intensity: ужасно
3. feeling: не хотелось
4. action: выходить под дождь
5. contrast: но
6. result despite that: я всё-таки пошла за книгой

You could move some parts for emphasis, but the original order is probably the best one for a learner to remember.

Because the correct spelling is всё-таки, with ё.

In many printed texts, Russian often writes е instead of ё, so you may also see:

• все-таки

But the pronunciation and meaning here are those of всё-таки.

For learners, it is helpful to remember the pronunciation as approximately:

• vsyo-ta-ki

Using ё makes the stress and pronunciation clearer.