headstrong
adj.having a strong will and not easily changing your mind. You use this to describe someone who is very determined, even if others think they are being stubborn.
adj.having a strong, independent will; not easily persuaded to change one's mind or course of action. Often carries a slightly negative connotation of stubbornness or recklessness.
“He is a headstrong person who never takes no for an answer.”
“Despite the warnings from his advisors, the headstrong leader decided to proceed with the risky investment.”
“The headstrong protagonist refuses to be swayed by the counsel of his elders, choosing instead to forge his own path through the treacherous landscape of the novel.”
From Middle English heedstrong, equivalent to head + strong.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.