sometimes we train using 'live' blades, that is, real steel blades with blunt edge. But although it's blunt, and we know it, the feeling is different compared to when we trained using tanto. The first time I trained against steel blades i did the technique rather sloppy, i ask my teacher because i usually don't have any problem when trained against tanto. That time my sensei said that perhaps i underestimate the tanto, feeling that the tanto wouldn't hurt me i can move easily, but when my partner hold a steel blade that might hurt me i was scared, doubted and thus move lousily.
here i also like to put a reminder o ourselves that we should treat any attack seriously, even if it is just a shomen uchi we should treat it like the cut is a sword cut, bottle, steel bar or else. This way we can do the techniquecorrectly and also built humility because we respect the attack.