There are a number of factors that may cause this but in my experience driving too fast is by far the most common. Instead of being planted at the proper depth and under our band of starter fertilizer the seed bounces out of the row, away from the fertilizer, and on top of the soil. While these seeds may still sprout, they are less likely to thrive. This is because of poor seed soil contact, risk of predation, risk of drying out, and lack of ideal fertility. Small seeds planted shallow pose the biggest challenge with seed bounce but once we slowed the drill back down it nearly eliminated stray seeds.