“Anything worth writing about is worth explaining. But you can't make something clear to someone else if it isn't clear to you. Before you write about a subject, make sure you know it inside out. If there are questions in your mind, don't skip them or cover them up.”
“Whenever there's something wrong with your writing, suspect that there's something wrong with your thinking. Perhaps your writing is unclear because your ideas are unclear. Think, read, learn some more.”
(Patricia T. O'Conner: Words Fail Me. Harcourt Brace & Co., New York, San Diego, London, 1999)
Replace “write” and “writing” with “translate” and “translating”: these statements still hold true.
Many inexperienced translators, and even several that should know better, follow what we may call “the school of magical terminology management”. They believe that what's important is to know the right name for a thing, not to understand it. Like in magic - where knowing the true name of someone means having power over him - in magical terminology, knowing the true name of something means you can translate it, even if you don’t really understand what it means.
Of course, magic doesn't work in the real world, nor does magical terminology: to translate correctly we need to understand how things work, what the author is trying to say, how to follow the instructions given in the original. If you understand them, you'll be able to translate correctly even if you cannot find how a particular piece of hardware is called in your language. If you don’t understand and cannot follow them, it does not matter how many terms you might have found: your translation will fail. If you cannot understand the original, neither will your readers understand your translation.
Not understanding the source text also means not being able to see where the source text goes awry. It means not being able to ask the right questions to the customer: if you are not clear about what you know and what you don't know, you'll be afraid of showing your ignorance, and will end asking too little, or the wrong question. It means failing to spot when the source text is ambiguous on purpose, or where the translation should differ from the original.