Be set on something/on doing something
Definition 1 of 2
Pro Tip 1/3Strong Intention
Shows a person's strong determination or resolve towards achieving something. 
He's set on becoming a doctor, no matter how hard the studies are.
Pro Tip 2/3No Alternatives
Indicates that someone is fixed on a single course of action without considering other options. 
She's set on starting her own business, even though her parents advised against it.
Pro Tip 3/3Potential Opposition
Can imply a person's decision may face opposition or is contrary to advice given. 
They're set on traveling despite the storm warnings.