You get to a point where you flex the plane to task without thinking. Your body aligns itself intuitively to the work and your muscles actually relax as you plane. This is good because planing is not really a rigid and muscular task but one of relaxed connection to the work transmitted more gently to the brain and by this sensing we microadjust our bodies and the pane to the work. A lot of the time I see students and apprentices bulldogging the plane to the edge of the board, which always creates its own problems. I suspect that may be happening here is that you land the plane at the start with a little more hesitancy and lack of confidence, then, once safely landed, you move more confidently down and along the runway before taking off as early as possible, not realising the full cut is incomplete or you relax the pressure too soon. The certainty I talk pof will not usually happen straight off the bat. It takes time to master skill and so i encourage you to practice wherever you can.