word choice in phrases

Why does one use the word "lo siento" rather than " estoy siento"? Why does one use the word ¿estás de vacaciones¿ rather than ¿estás en vacaciones¿

Here's one even I can help with! :oops: "Lo siento" literally means "It I feel". I remember it by equating it with the English thought of "I feel your pain" or "I feel I've hurt you". The literal meaning of "Estoy siento" would be "I am I feel" or something along those lines. As you can see, it doesn't make much sense in Spanish or English. I'd like to know the answer to the 2nd one myself.

The best and most simple answer that I can think of is: Don't question it, just accept that it is said that way. Don't waste your time trying to translate directly from one language to another. For instance: the most common way to say "you are welcome" is "de nada" which literally means "from/of nothing." Don't waste time trying to figure out the word for "you", "are", and "welcome." Trust me, whatever you come up with, will make you sound silly in Spanish.