Sometimes I think about alternative paths I could have followed vocationally and the steps I would take to get there if I were much younger and making that choice now. It's almost like creating a new character in a role-playing game: "I'll start off as a economics undergraduate and then after five levels I'll switch to the prestige class Austrian Economist and go on a quest for Bigby's Prize in Honour of Alfred Nobel".
In RPGs, if you feel your character "concept" isn't working, you can go back and start a new one. Of course, that's much harder to do in real life, although some people do go back to undergraduate studies for a complete change in career.
I'm clearly multiclassing in real life. After getting a couple of levels in Mathematician, I switched over and progressed three or four in Linguist. Then I went and levelled up in Technologist a good eight or ten levels (the first few specialising in the schools of Web and XML but then also adding Python and Open Source). Somewhere along the way I picked up a level in Filmmaking and a couple in Music.
Progression as a multiclass character is much slower because you're a jack of...no...a journeyman of some.
Oddly enough, very few of my pen-and-paper RPG characters have ever been truly multiclass. They've either completely been in one class or had a few initial levels in one then made a permanent switch.
I think I'm attracted to the singular focus of just one class but, without the ability to go back and start a new character in real life, I've decided multiclassing is the way to go for me.