When a hitter is 0-1 against the pitcher, the chances of him getting a hit decrease to 22%.
Meaning 78% of the time he will make an out!
When the hitter is 1-0 vs. the pitcher, this puts him in a more comfortable situation where us as pitchers now have a tougher time getting him out. Percentages say that hitters starting with a 1-0 count have a 32% chance of getting a hit.
Thus making him a .320 hitter. These numbers are on a big league scale but are relative to any level.
Make an effort and purpose to pitch ahead in the count by getting "STRIKE 1!"