Either not flossing enough or using bad technique. I'm not a big flosser, so my gums always bleed a bit when I do it myself, but my dental hygienist always flo

Either not flossing enough or using bad technique. I'm not a big flosser, so my gums always bleed a bit when I do it myself, but my dental hygienist always flosses me after a cleaning and she never makes the gums bleed.