A slightly touching faith in the Met Office.
Given that all the winds they give you are wrong, you are ill advised to fly by dead reckoning. Your forecast wind just gives you an assessment of fuel required and potential problems en route eg too much cross wind on landing.
You actually fly by pilotage. You compare your map with your track required and timings. You are judged by arriving within 2 mins of your ETA but not the ETA you got from your plan but rather the one you get from your pilotage assessments.