I am so sorry about the title.  I am a child of a certain generation.

I deal a bit with XML in my day-to-day and "getting" XSLT was a pretty significant step forward in this for me.

Doug Tidwell's book XSLT was the key.

What prompted this revolation was seeing that XSLT was more than just a way of rendering XML to HTML in a browser, but that XML to XML translations can be exceedingly powerful.  Right now I am dealing with a data source that has been flattened from a normalized relational structure, and now it needs to be put back together into a third, different structure.  All this is do-able.

FWIW, my tool of choice currently for XSLT development is Architag's XRay... but I still prefer WMHelp's XML Pad for general day-to-day XML editing.