Interesting fact that will help you understand this crooked driver straight iron thing, research the D plane,
Readers digest is that Irons are hit with a decending blow while Drivers are hit with a level to ascending blow. To hit the iron straight requires that the club head exit impact slightly to the inside but if you do the same with a driver you get a fade or slice because the angle of attack is different, driver needs to exit impact more toward the target, hence the saying let the big dog eat.