Breakdown of Mi novia se puso a seguir el tutorial, pero acabó siendo frustrante.
ser
to be
pero
but
mi
my
la novia
the girlfriend
Questions & Answers about Mi novia se puso a seguir el tutorial, pero acabó siendo frustrante.
Why is it acabó siendo instead of acabó ser?
To express that something "ended up" a certain way, you must use acabar followed by a gerund (siendo), not an infinitive. You cannot directly attach an infinitive to acabar to get this meaning.
Could I use acabó por ser in this sentence instead?
Who or what is the subject of acabó in the second clause?
The subject changes midway through the sentence! The subject of se puso is Mi novia, but the hidden subject of acabó is "it" (the tutorial or the situation). We know this because the sentence says it ended up being frustrante (frustrating). If the girlfriend were the subject of the second half, it would say she ended up frustrated: pero (ella) acabó frustrada.
Why does the sentence use se puso a instead of just empezó a?
Both mean "started to," but ponerse a + infinitive is a very common periphrasis that implies someone actively, deliberately, or energetically "set about" or "got down to" a task. It sounds much more natural here to describe the focused, intentional effort of following a tutorial.