Novel: When his critically ill mother tells him to stop drifting through life, a penpusher leaves his entire life behind to go on an adventure and pursue his dream of finding a legendary animal in the heart of south america.

I don't care for "drifting through life."

When his mother falls critically ill, a secluded son undertakes her life-long quest to find a legendary animal located in the heart of South America before she dies.

So how could I make this work? By changing the reason he wants to go on the adventure and forget about the mother?

So basically, it's the deceased mother's story? That's a red flag.