Health behaviour is often broken into knowledge, attitude and practice. To answer, ask which of these is the one a person actually performs and which therefore needs a push to happen.
Knowledge is information held in the mind and does not by itself move a person. Belief is a conviction, again an internal idea. Attitude is the emotional leaning toward or against something; it has feeling attached but is still a disposition rather than an act.
Practice is the doing. Translating what you know and feel into a real action is where motivation matters most, because people frequently know the right thing yet fail to do it without a reason to act. So practice is the component most strongly shaped by motivation while also being tied to emotional drive.
\[\boxed{\text{Practice}}\]