Even if your web site is filled with pictures, the most critical information is probably conveyed by words. This is particular true for interactive elements like navigation links, buttons, and form fields. So, why should you care about that?
In graduate school my studies focused on the psychology of language and I've also taught a course on it for many years. If I had to choose the most important big idea about language, it would be that language is highly ambiguous. Many students who come to my class have the misconception that a sentence like the one I'm writing right now has some kind of inherent meaning, and that meaning exists separate from any particular person who writes or reads that sentence. That leads us into all sorts of debates and arguments about what a particular passage of text "means," where we say things like "What that sentence actually means is..."
The thing is, that's a fundamental misunderstanding of how language works. Language is first and foremost a tool for influencing the thought and behavior of other people, which is why philosophers of language talk about "speech acts." And most of the time, it's much more important to consider what the speaker's goals are than what a sentence "means."
For example, if we're having dinner together and I ask you "Is there a salt shaker at your end of the table?", I would probably be irritated if you said "Yes!" and then proceeded to butter your dinner roll. That's because I expected you to think about what I wanted, not what I literally was saying. Of course, what I want depends heavily on context. If I'm setting up tables for a wedding reception and I want to make sure there's a salt shaker on every table, then the appropriate answer to my question would indeed be "Yes!"
So the way language actually works is that we are constantly trying to use the words a person says to help us make an educated guess about what it is they are after, and we use our own knowledge, our knowledge about that person, and the context to help us make that guess.
In case you're wondering if this happens other places than the dinner table, here's part of a follow-up message I recently got from a seller after making a purchase through Amazon:
What the person writing this message wanted was for customers to contact them before posting a negative review. But if you read carefully, they never directly say that. They are relying on the reader to fill in the blanks and figure out what they really mean. For that reason, this statement, along with the question about the salt shaker, is called an "indirect speech act."
Once you start looking for them, you'll find that indirect speech acts and other forms of ambiguous communication are everywhere. They are a natural part of how we use language, and it's virtually impossible to avoid them. However, they can also lead to confusion or misunderstandings. This is especially true with written communication like e-mails and web sites where we are missing all the non-verbal cues that help make the intended meaning clear (think of sarcasm) and also help us know when communication has broken down.
As a writer, it can be difficult to know when we've written something confusing or ambiguous. Remember, we normally handle ambiguity by considering the context and making use of our background knowledge. And we do this automatically and unconsciously. As the person writing a message, we use our own context and background knowledge. But those may not be shared with the person reading the message.
Here's an example to illustrate that point. Consider web sites of health insurance companies. These sites have multiple audiences, so they typically have a way to indicate what kind of visitor you are, so that they can show you the content appropriate for that role. The images below show what that looks like on several different sites:
Three of these sites use the term "Producer" in the set of options. When I first saw this, I had no idea what that meant. It wasn't until I saw other sites that talked about brokers and agents that I started to understand. Googling "insurance producer" confirmed that this means people who sell insurance. For people who work in insurance, I'm sure this is common knowledge. But it's not common knowledge in the general public. So why use this term on a consumer-facing site? I can't know for sure, but my guess is that the people who created these menus didn't think the term was hard to understand - because for them, it wasn't.
How can you avoid these kinds of problems on your own site? Well, how would you catch them if you were, say, writing an article or report? You might ask someone else to read it and mark any parts that seemed unclear. In the case of a web site, we can do a similar thing with usability testing. Put your site in front of the people who will actually be using it, and give them specific tasks to do. Then watch, not just for where they outright can't do the tasks, but where they hesitate for a moment, or click around trying to find something.
Quite often the issue has to do with language use, and the user not understanding a word or phrase the way you intended it. And in those cases, you can try to find a way to communicate your meaning more clearly, for example, by saying "agents and brokers" rather than "producers." You won't be able to eliminate ambiguity altogether. But paradoxically, the more aware you are of how ambiguous language can be, the less likely that your messages will end up being ambiguous.