mnlg:

Stefano B:So I guess I still don't why the verb cannot take a direct object simply because it is defined as "to be lacking/missing".

The sentence "I miss my pen" seems to have (at least) two distinct meanings, roughly "I wish my pen was with me" and "I fail to hit my pen".

I think you misunderstood me. I wrote "I am missing my blue pen", not "I miss my blue pen". Those two statement mean different things.

The statement "I'm missing my pen" or "I'm missing a thousand dollars" means that you should have that particular object, but you don't. You've lost it, you lack it. It has nothing to do with yearning to see someone/something.

For example, if I'm away from home and I miss my family, I'd say "I miss my family. I haven't seen them for several weeks".

I wouldn't say "I am missing my family", that gives the impression that the family is lost and you don't know where they are.

mnlg:
In Esperanto they are translated as "mia skribilo mankas al mi" (or perhaps "mi sentas mankon de mia skribilo") and "mi maltrafas mian skribilon".

Not necessarily transitivity is preserved across languages along with the general meaning.

This goes both ways; consider for instance "I listened to you" and "mi aŭskultis vin" (direct object in Esperanto, not so in English)

I'm kind of confused now. What does maltrafi mean? The Lernu dictionary just says "miss" which doesn't help me at all, because "miss" can mean different things.

Stefano B:I'm kind of confused now. What does maltrafi mean? The Lernu dictionary just says "miss" which doesn't help me at all, because "miss" can mean different things.

"Trafi" means to strike or hit. "Mal" always makes a word mean the opposite when it's tacked onto the front of it. So, "maltrafi" would mean to miss in the sense of not hitting.

When confronted by a "mal" word , it's often very helpful to take a look at the "non-mal-ified" root in order to clarify its meaning.

Stefano B:The statement "I'm missing my pen"

"Mi ne plu trovas mian skribilon".

I'm kind of confused now. What does maltrafi mean?

"miss" as in "failing to hit".