Though the majority of this text is very basic reading, there are three phrases which jump out at me as being difficult, or words I couldn’t find in basic dictionaries.
理所应当 – lǐ suǒ yīng dāng This phrase means to feel something is well-deserved, that something has been earned through hard work, usually when it actually hasn’t. So I guess that roughly translates to ‘taking a reward for granted’? In this story, Monkey feels that his payment is well-earned or well-deserved. But as readers, we know Monkey doesn’t deserve anything at all – he’s taking that payment for granted when he didn’t really earn it. Consider this phrase in another context:
别人帮助你那是义气，你不能当作是理所应当的。 – “When other people help you it’s in the spirit of self-sacrifice, you shouldn’t consider this something you deserve as a matter of course.”
甜头 – Though this looks like two words, the first meaning “sweet” and the second meaning “head” or “brain”, it’s actually a colloquialism that just means “sweet flavor” or “pleasant taste”.
贪念 – These two characters also seem separate, they don’t appear together in my dictionary, but they’re actually one word. According to Baidu Bai Ke, the Baidu dictionary (a Chinese-language resource for word meanings and derivations), 贪念 tān niàn just means “greedy” (I presume the “念” probably adds the meaning “idea” or “thoughts” here, so 贪念 could be read as “greedy thoughts”).