Same story for sophomore, same story for junior year, I finally took it senior year because they wouldn't get another chance even though it still doesn't fit in the workload ha ha.

大二，大三都是如此，最后我到大四才来上这门课,因为即使学业再忙,再不选就没有机会了，哈哈。

哈佛公开课 - 计算机科学课程节选

I'd say the major difference is probably the workload.

让我说主要的区别在于工作量。

做交换生来到这里 - SpeakingMax英语口语达人

Perhaps a mistake with some of the answers we got but one of our choice favorites was this one and it's actually fairly worth drawing one's attention to and that's this: I planned on taking the class as a freshman then convinced myself otherwise because I couldn't fit it into my workload.

得到的回答或许有的是错的,我们最喜欢的一个回答是这样的,值得我们注意一下：,我本打算大一就来上这节课,但却说服自己还是别去上了,因为我工作负荷满满的。

哈佛公开课 - 计算机科学课程节选