I am still allowing myself to make an occasional mistake, because if you do not read the ingredients carefully it can be hard to say what is (for example, finding out a brand name chicken ramen bowl is artificial chicken and is actually vegan friendly) and what is not vegan (for example, a brand name candy I previously enjoyed, sadly), but rather than giving up I hit the reset button and start again the next day until I get it right. Everyone gets a mistake!

Doing less than 100% is not a "mistake." Self-castigation only undermines your efforts. The change you do make still matters. I have started aiming at 80% because it is attainable. Doing so sets an example for others that it doesn't need to be a radical lifestyle change, which in net terms may be more effective than doing 100% but scaring people off by making it look unattainable and uncomfortable.