noun
foolish plan; ill-conceived scheme
Refers to a plan that is objectively unwise or poorly thought out. Not necessarily humble; can describe anyone's plan.
彼の愚計はすぐに見破られた。
His foolish plan was quickly seen through.
noun
my humble plan; one's modest proposal
Humble language (kenjougo) used to refer to one's own plan or proposal in a self-deprecating manner. Often used in formal or business contexts.
愚計ではございますが、ご検討いただければ幸いです。
This is my humble plan, but I would be grateful if you would consider it.