So theoretically, one can avoid mortal sin (and the possibility of hell) by driving through McDonald’s and picking up fish sandwiches for dinner, or going out and indulging in sushi.
Why does it have to be so complicated?
If you casually pick up a fish sandwich, you do nothing for your greater conforming to the image of Christ, Who chose to give up his life for you. However, you do not defy the Church that asks for some token self-denial. You do not do anything heroic even is the slightest degree, but you do not commit a mortal sin either.
Where is the complication?