It is the reason of my doing sth that...... instead of......
It is the reason of my getting up late that I've had a bad cold instead of staying up yesterday.
例句:我晚起的原因不是昨天熬夜,而是得了重感冒
用it is句型,不会头重脚轻,且强调了某事发生的真正原因,符合英语重点在前的习惯
望采纳
The reason I do it is for some other thing instead of this one
The reasons for which we do sth. are not for sth. but for other things.
I have reason to do sth not because of something, but because of sth.
我做某事的原因不是因为某事,而是因为某事。