You've probably had an experience like this: you're trying to remember someone's last name, and you think to yourself, "I don't remember what it is, but I know it starts with a K."
This seemed weird to me the first time I really thought about it. If you don't know the name, how do you know what letter it starts with? But our memory may be more like a network of associations than a computer memory that stores exact data. So this no longer puzzles me. Instead, I've been thinking about the following variations . . .
How many times have you had this experience? You're trying to remember someone's name, and you think, "I don't remember what it is, but I know the second to the last letter is a T." Probably never, right? What about, "I don't remember what it is, but I know it had three vowels and six consonants." Never, right? Why is that? What is so special about the first letter, that we are more likely to associate a word with its first letter than with some other fact about the word? Is this a learned behavior, based on all those "Z is for Zebra" type of phrases we saw when we were learning to read?
When we try to remember a complex phrase, we might make up an acronym out of the first letters of the words, but we wouldn't try to remember the pattern of the last letters of the words. Why not?
When Japanese people forget words, do they often remember the first kanji but not the second or third? I don't know the answer to this, but somehow I doubt that it works that way. It seems like something to do with alphabetic writing.