麻痹大意 [- - dà yi]drop one's guard; be careless and unconcerned; lack of vigilance; be off one's guard; insensitive and negligent; neglectful; be caught off guard; let one's vigilance be lulled; lower one's guard and become careless; slacken [relax] one's vigilance:
•¶ 不能因为没发生什么问题就麻痹大意起来。 We can't get unwary just because nothing unusual has cropped up.