Snow bunny: mistakes happen, and perfect people do not exist on this earth. Totally not believing in Hashem chalila, is far from similar to tripping up.
This does not exempt us from trying harder, and with most Shabbos “mistakes” you can institute “fences” so that they don’t reoccur. Changing out the tissues, covering light switches, putting away muktzah stuff etc. are good ideas to implement for everyone, especially those that are not “in the habit” yet or absent-minded. Hatzlacha!
As a side note, did anybody find the “aveirah” video done by yeshiva bochurim, presumably for purim, offensive? Before reading the details I thought it was done by otd guys.