have (or know) all the answers
informal Be overconfident about one’s knowledge of something: it was his air of knowing all the answers which riled Mrs Farrar...- Her article is more in the nature of sharing her problems and frustrations in trying to understand the complexities of rural poverty rather than an assertion that she knows all the answers.
- Obviously there are going to be people who know all the answers and others who don't know anything.
- Doctors are just as much in the dark as parents and often less wise because they think they know all the answers.
See parent entry: answer