In the late 90s, when I began making webpages, there was a mysterious folder in my shared hosting FTP account called "cgi-bin." What is "Bin." I was on Windows. What is "CGI." A friend told me it had something to do with Perl. I didn't know anything about Perl, and everything I found on the web about it was difficult to understand.
After some experimenting with FrontPage extensions, I began to experiment more. I found a site called Matt's script archive that had Perl CGIs that I could actually understand. It was slow, slow going. I was coming from QBasic. I scoured the Web, mixing and matching bits of example code I'd found to make things like random quotation generators. Then a friend showed me something called PHP.
PHP, to me at the time, wasn't just a language - it was an ecosystem of developers, example code, and practices that was flourishing. There was consolidated documentation. There were global functions for any string operation I could conceive. But most importantly to me at the time, there was an active community who was interested in more than showing off their most arcane, clever, and obfuscated programs. Very early on, the PHP community could be characterized as "welcoming."
I would argue that PHP "won" not because of any innate technical superiority over any of the other languages available for web programming in the mid to late 90s. It won because it had the right kind of community for a new breed of developer - the "web programmer." It didn't have the stigma of snootiness that came with trying to figure out Perl. PHP was not for geniuses or academics; PHP was for people who wanted to make dynamic websites and not have to catch attitude from some asshole in IRC about not knowing what tail recursion is.
I don't use PHP anymore. I don't like PHP any more. I got into Java, JavaScript, C, even Prolog; and now, I'm into whatever will save me time, and scale. Language agnostic. I'm into parallelization and web services; why would I use PHP for anything more than toy projects? Yes - PHP is "easy." But at my current (thankfully temporary) job, I'm in charge of adding features and debugging a massive functionally-written PHP codebase. It is horrifying.
I think PHP is a great language for anyone to learn how to program with. I think there's a lot of shitty PHP code out there and it's easy to make a living by billing yourself as a PHP developer. It introduced me to "C-like" syntax of brackets and semicolons. It's an easy way to learn how to do neat things with SQL. Beyond that, it really just sucks, and no matter how much more crap they add on to it, I think it always will.
So what is the lesson here? PHP won because it had an excellent community. The Ruby/Rails uprising of the past few years reminds me a lot of the early PHP days. PHP made it easy for independent, inexperienced programmers to create dynamic web applications. Which was great. But having grown up and seen the world, I've rarely seen or worked with small teams of professionals, fluent in several languages, who have decided that PHP is the best way to implement a website. But hey - whatever floats your boat.