Special occasions make this feel impossible

Can you eat at your deficit throughout the week and then eat at maintenance on the weekends?? Lots of people do this and still lose weight from their weekday deficits.

Yes the weight loss will be slower, but you'll still lose weight!

A small piece of cake is about 400 calories. Surely that isn't going to ruin everything.

I think it's easy to get into that "all or nothing" mindset, but if you actually look at what you are telling yourself it doesn't make sense.

Everyone has life-parties. You have to be a little flexible. Maybe skip breakfast that day. Maybe skip breakfast the day after. Whatever...it's easy to make up 400 calories. Take a half hour run. . .

I have gone to so many parties where I ate several pieces of celery, 4 baby carrots, and a decadent dessert. If it's happening every week, maybe that's a really bad idea. But once in awhile, not a problem.

Log all of it.

I often bank calories during the week for more indulgent weekend events. As you described, family bbqs, parties, dinners out often happen Thurs-Sun for me. So I often bank 100-200 cals less during the week to have 500-1000 cals extra on the weekends. It's the total calorie deficit over time that leads to weight loss, not coming in at or just under goal every single day.

What are your stats, goal, and current goal rate of loss? Often people take an extreme approach, trying to lose the weight as fast as possible and thus choose to cut calories aggressively, which doesn't leave room for foods you enjoy, and often isn't sustainable.

Also, do you exercise? Do you eat back the calories from exercise? You may want to think about factoring in something extra on days when you have those special events, to give yourself even more wiggle room.

Bottom line, this is supposed to be a lifestyle change, and all those things you described are part of your life. The best thing you can do is figure out how to still enjoy those events AND achieve your weight loss goals. Thinking that you've blown your diet and you might as well eat everything in sight is not a long term strategy. Allowing yourself to have a small indulgence without beating yourself up, is...

It's life. If you want to keep the weight off, you'll need to adjust your thinking. You'll need to think about how much you eat for the rest of your life. There will always be a vacation, or a wedding, or a birthday. If keeping your weight stable is important you'll figure out how to plan ahead.

Something I had to learn to keep from blowing my deficit every weekend: occasions that occur every week are not special occasions. Also, some occasions that are special for someone else (friend's birthday) aren't necessarily special for me.

If feeling bad about ourselves caused weight loss we'd all be skinny. So, stop it. Stop punishing yourself for leading a normal life. To lose weight, one needs to eat at a calorie deficit on average over the long term. For some of us that's more difficult than for others. That's not a moral failing that's just life.

You've decided to try to eat at a deficit over the long term. You have identified an aspect of your life that's making that difficult. Now you get to decide what to do about it. The birthday cakes are getting in the way of your calorie deficits. Choose. Eat the cake and either have less of a deficit or increase your deficit on other days to make up for it. Or don't eat the cake. Whichever you choose is your decision.

Nobody is perfect. In fact, no one really knows what perfect is! So stop judging yourself on some mythical ideal. Controlling how much you eat is hard enough without setting traps for "moral failure."

If I had frequent special occassions, birthday parties, etc., I wouldn't eat the cake every time. Instead I would wait until there was a cake that looked exceptionally delicious, as most party cakes are pretty terrible IMO. Unless you are surrounded by fantastic bakers and chefs, my guess is that you are more in love with the idea of cake than the actual taste of most of the cake you eat. My only suggestion would be to be stingy about what you spend your calories on.