The headstrong impetuous man rushed into things without forethought.

这个顽固的莽汉，不预先考虑，仓促行事。

youdao

He says most gun deaths are classified as manslaughter, which implies a crime committed without forethought.

BBC: US gun debate: Could Obama's guns plan work?

But Mr Bush's barging into Iraq without adequate forethought has resulted in a debacle.

ECONOMIST: America and Iraq