>Does anybody have difficulty in expressing their thoughts in written form?
Used to. My experience was basically:
>internet is becoming mainstream
>have the composition skills of a high school student
>get savagely BTFO on a BBS
This happened quite a bit, as you might expect. I was inserting myself into a venue of older and more experienced people. Of course I'd look like an ass.
And yet, it was necessary to put in the practice, and to grasp the essence of the problem. I got my hands dirty over and over, scrapping with strangers and being deeply vexed, and eventually things began to click. I developed my style, learned to tune my message to the person I was talking to, etc.
It was a lot of elbow grease to get to the point where I could rattle off a post fluently, and even now I find that an indifferent effort toward editing garners an indifferent reception.
>I mean i can form an argument in my head; I can read perfectly fine, but when i want to write something, my mind goes blank. all the vocabularies i know disappear
>from my pathetic head
It sounds like you have the mental machinery to articulate yourself well, but you also strike me (just from that "pathetic" bit) as someone who suffers the problems that modern schooling often produces: anxiety, vulnerablity to criticism from strangers, and a fear of failure that makes you seize up when you try to do something a little above your skill level.
And that, of course, is just one boomer's off the cuff inference from a few lines of text, and I could be wrong. My advice, regardless, is to just practice more; keep a journal and write a little each day to practice putting your thoughts in order. It's also important to practice well, so take some care to revise your writing, and you will probably improve quickly.