Breakdown of Ein gutes Buch kann einen wirklich motivieren.
ein
a, an (eine)
das Buch
the book
gut
good / well
können
can / to be able to
Questions & Answers about Ein gutes Buch kann einen wirklich motivieren.
Why use einen here instead of man?
man is only used when the general 'you' or 'one' is the subject of the sentence (the nominative case). In this sentence, the book is the subject doing the motivating. The person being motivated is the direct object receiving the action, so we need the accusative case. The accusative form of man is einen.
How do I know whether to use einen (accusative) or einem (dative) here?
It depends entirely on the verb. The verb motivieren takes a direct object in the accusative case. If the sentence used a verb that requires the dative case, like helfen (to help), you would use the dative form einem instead, for example: Ein gutes Buch kann einem helfen.
The translation says 'motivate you'. Could I just use dich?
You could absolutely say Ein gutes Buch kann dich wirklich motivieren if you are talking to a specific person. But using einen makes it a general statement that applies to anyone in the world. In English, we often use 'you' for this general meaning too, which is why the translation looks like it could be dich.
Why does the adjective in Ein gutes Buch have an -es ending?
Buch is a neuter noun (das Buch). Because the indefinite article ein has no ending in the nominative case to show this gender, the adjective has to step up and do the job. It takes the strong neuter ending -es.