Breakdown of Mój ołówek sam się złamał.
się
oneself
mój
my
sam
alone / himself (emphatic) / pure / nothing but
ołówek
pencil
Questions & Answers about Mój ołówek sam się złamał.
Why is there a się here? Couldn't I just say Mój ołówek sam złamał?
No, you need się because złamać on its own means to break something else. When an object breaks spontaneously, Polish uses the się form, like złamać się, to show that the action happened to the subject itself rather than being done to a direct object.
If się złamał already means the pencil broke, why do we add sam?
You don't strictly have to! Mój ołówek się złamał perfectly translates to "My pencil broke." Adding sam adds emphasis, exactly like saying "My pencil broke all by itself" in English. It stresses that nobody was touching it or causing it to snap.
Why is it sam and not sama or samo?
It has to match the gender of the noun it refers to. Ołówek is a masculine noun. Therefore, the word for "by itself" must take the masculine form sam, just like the past tense verb must take the masculine ending to become złamał.
Could I use zepsuł się instead of złamał się to say my pencil broke?
Not really. Zepsuć się is usually used for machines, electronics, or systems breaking down, like a car or a phone. For rigid objects that physically snap in two, like pencils, branches, or bones, you should use złamać się.