Commencement speech Steve jobs I

Today, i start to read commencement speech about of Steve jobs in internet. The text is about Steve jobs commencement speech at Universitie of Stanford in 2005. 

He tell graduate three stories from his life. The first story is about he dropped out of Reed college after the first six months. But he did not really quit the college, he stayed aroud as a drop-in during 18 months.

So why did he drop out??