rotary cutting

just a note about rotary cutting...as i was on my way home from work, i realized something i had been doing wrong. as i slide the rotary cutter up the ruler, i always push the blade into the ruler, which inevitably pushes the ruler to the side or pushes the fabric under the ruler. once i could get the hang of pushing the rotary cutting straight down, using the ruler as a guide, i was good to go...sounds simple, eh? one would think...