by the seat of your pants by instinct rather than logic or knowledge. informal

☞ This expression was first used by pilots in the mid 20th century, in the form fly by the seat of your pants, meaning 'fly a plane by relying on human judgement rather than navigational instruments'.

1977Martin WalkerNational Front Mussolini had governed by the seat of his pants, guided in part by his early Socialism, in part by his…bombastic nationalism.