You use hard-headed to describe someone who is practical and determined to get what they want or need, and who does not allow emotions to affect their actions.
1. unreasonably rigid in the face of argument or entreaty or attack
2. guided by practical experience and observation rather than theory;
"a hardheaded appraisal of our position""a hard-nosed labor leader""completely practical in his approach to business""not ideology but pragmatic politics"