The Gemoro says (Brachot 9b)
dayah letzarah beshaatah. The way I understand this and I think Rashi learns like this as well, is that there is no point worrying about an upcoming Tzarah. If you can do something to stop the Tzarah, then do it. If you cant, then do nothing. But either way worry and fear is pointless.
If this is the case, how to we understand how the Gedolim all trembled in fear of the Yom HaDin? Of course, Teshuva is very important especially if one doesn't want to suffer the consequences of Onesh HaDin. But why were they scared. Whatever will be will be. They should make themselves the best plan of action, but should not be experiencing emotions such as fear and worry; they should be telling themselves
dayah letzarah beshaatah.
Do not answer my question that the reason why they are scared is because it helps Teshuva. I understand how fear would help the Teshuva process, but they shouldn't be able to get to that fear. Their supreme knowledge and wisdom should stop their fear which they are trying to attain by saying,
dayah letzarah beshaatah?