I love this thread because it gives so much personal insight into other people's motivation to make the Esperanto journey. Reading what inspired other people to learn Esperanto made me want to crystalize my own reasons for studying the language.
First of all, I fell in love with the idea of studying a language that you really could learn on your own from a book and be able to communicate with people from a multitude of different languages and cultures. Unlike any other language, people who learn Esperanto WANT to communicate with others. What if I decided to study the language of another country? I could study Lithuanian, Latvian, or Bulgarian and practice until I was quite fluent---but then what? I couldn't just show up on the streets of Lithuania, Latvia, or Bulgaria tomorrow and start talking to random people--they'd think I was weird--but more importantly, even if I did have people to communicate with, I'd be locked into just that one country. Esperanto makes it possible to truly have an international circle of contacts.
Secondly, it keeps me fresh as a language teacher. I'm a Spanish teacher as well as a translator, and even when I'm not in the classroom, I find myself using Spanish on a VERY regular basis. It would be a rare day, indeed, that I didn't use Spanish for some ordinary reason. Because Spanish is such a normal part of my life, quite honestly, it was hard for me to remember what it was like to be a beginner and to attempt to use a language in which I was not yet very fluent. Studying Esperanto gave me the opportunity to go back and revisit what my students go through when they first start acquiring a second language.
Currently, I'm a Ph.D. student studying language acquisition. There are so many theories out there about all the different facets of developing language skills: the role of grammar and how it is acquired, how people develop fluency, how people negotiate meaning, etc. Most of us acquire our Esperanto skills in segments--we have to wrap our brains around the word building features, we have to learn how to navigate the grammar (particularly the use of active and passive participles that show past, present, and future aspect), and then we STILL have to develop oral fluency and comprehension skills---Esperanto gives people the opportunity to fully appreciate each individual segment of the entire language acquisition process. I often find myself reading material about some aspect of developing skills in another language and relating it to some feature of Esperanto or of my experience learning or using it.
Finally, learning and using Esperanto feels like belonging to an exclusive, unique club. We're part of a fascinating group of people who are just talented enough, or "nerdy" enough, or interesting enough--as well as motivated enough--to teach ourselves a brand new language out of a book or off the Internet or something, and then go use it. Most clubs don't have their own "secret", private language--we do!