The high-end expression of being confident can be "having a plan in mind" or "having an idea in mind". Both of these idioms mean to be fully prepared and confident about something.
1. Having a plan in mind: This idiom describes a person who has complete plans and ideas in mind before doing something, and is confident in the result. It comes from a poem by the ancient Su Shi, "If you have a confident mind, you can adapt to endless changes."
2. Know something well: This idiom means having a clear understanding and grasp of the development and results of things. It is often used to describe the calmness and calmness of experienced people when dealing with things.