My wife is Japanese and fluent in English but still almost always mixes up the and a. I think part of the problem is that it just barely sneaks under the radar

My wife is Japanese and fluent in English but still almost always mixes up the and a. I think part of the problem is that it just barely sneaks under the radar of a mistake that is bad enough to confuse English first language speakers in everyday use. So theres no impetus to correct it