WIY: I know that. Here’s the issue. In order for your teshuva to be good, you must make a firm commitment not to do the sin again. If you say, “I’ll do my best, but I’ll probably slip up,” it’s not very good. You must have a firm commitment to stop.
On Yom Kippur, it’s very difficult for me to make a firm commitment, knowing that I will almost certainly slip up again, very soon after Yom Kippur.
I just said, “I know that I will probably slip. I’m trying my best, but the Yetzer HaRah is very strong. You know I am doing my best, and I will likely slip again. Please judge me on my effort, not on the outcome when I fail.” Then, of course, we ask Hashem for mercy, not strict judgement.