On the how bit: there is no such thing as reading code once. It is a simple matter of reading a method/object/what-have-you, then rereading it until you see it

On the how bit: there is no such thing as reading code once. It is a simple matter of reading a method/object/what-have-you, then rereading it until you see it called/referenced etc and don't ask yourself "wtf does foo do". Trace various code paths often enough and you'll 'get it'. As for the why: I used to decide I didn't like module X, then decide I was going to implement it myself. After some time I would end up with something looking like X, but not nearly as refined. As such, I learned it's better to read others' code and understand it -- much faster than reaching the same conclusions as the original authors w/ crappier code. Of course if after understanding you decide you still think it's crap -- have at it :).