Jimmister, personally I don't think you did anything wrong there. If you weren't expecting anyone and weren't supposed to answer the door, what good would it have done to know *who* it was? Plus if they had seen you, do you think they would have given up that you weren't home? No. Anyway, it would have been more impolite to peek out, be seen and then *not* answer the door. There is no insult in finding that "no one is home". Its a big insult if they are home and deliberately avoiding you. And if sister was expecting someone, perhaps she shouldn't have been lounging around in the bath. Just because the doorbell/phone rings, doesn't mean a person *has* to answer it. Just my opinion, anyway.
I have had days when it felt that I couldn't do anything right either. Some days it does get to me too, especially when I was trying my best but it seemed not to be good enough, days where I was so proud of an accomplishment, only to have that ignored and have a perceived failing harped on . Some things I just made a mental note for later not to do again or do differently the next time, other times I wondered if this was going to matter next week - usually it will not. I try to remind myself of that if I am having a bad day.
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People think there are four elements to the world; fire, wind, water and earth. They are wrong. There is a 5th element - surprise. - paraphrasing of Terry Pratchett "The Truth"