Why is it a good thing to get scared for the Yom HaDin?

It says 'Day Tzarah LeShaatoh'! This means that there is no point in worrying about anything of which the product of the worry is futile. IE perhaps to plan a plan it is good to think about what could happen, but worry has no place. If the bad thing will happen, it wont help worrying. If it wont, why worry. This should be the pyscological stance of a clever person on the matters of fear and worry.

In that case how does it make sense to be scared of the Yom HaDin? Of course to plan is important, but what are you scared about. Whatever will be will be?

The fear is not pointless - rather it to instill in us the ability to do and daven for all good with all our hearts The Brisker Rav relates the following parable:

There was a man who earned his livelihood by smuggling illegal goods across the border from one country to another. He would have customers in different cities, that he would sell to once he got there. How did he actually transport the goods? He would hire an unassuming wagon driver, load up the back and settle down for the journey. The smuggler himself knew exactly what he was carrying and knew the repercussions of what he was doing. He understood he was committing a crime. A few hours before they would even reach the border he would begin to get extremely edgy and nervous, for he understood what was at stake. The wagon driver, on the other hand, had no reason to be nervous. As they approached the actual border the wagon driver would get a little nervous, naturally, for there were times when you can encounter a nasty border guard who could cause problems if he so desires. The only one, who had no fear at all, as they approached the border, was the horses. They were oblivious to what was going on, had no clue what they were carrying and unaware of the ramifications that could have existed should they get caught. My understanding is that those of us who understand the seriousness of these times will begin to "Worry" at the beginning of Elul, Those of us who are not so into it will only begin right before R"H, and then there are those like the horses who just can't wait for the food!!

From Rav Avigdor Miller ZATZAL - What impact should Rosh Hashanah have on us? We are afraid of the great judgment of Rosh Hashanah. Not only we are judged for the year to come, we are judged what's going to be afterwards, the rest of our lives and after our lives. The pachad (dread) of the Yom Hadin (Day of Judgment) has to enter the marrow of our bones. (#E-201, Fundamental Principles)

I would like to suggest that it is the Awe that we dread, not the actual fear of what could happen. And Awe doesnt go away with Day Tzaroh Beshaatoh