Why do low-key, humble Christians often feel more authentic than outspoken ones?

In my whole life so far, I have noticed how most of the Christians who constantly talked about how they are saved and can do any sin and still go heaven, the ones who go to church a lot, people on their cars Jesus stickers, etc are the most hypocritical Christians and are the ones who constantly doing horrible sins yet judging other people's sins. On the other hand Christians like my grandma till this day is a great Catholic and person and doesn't constantly talk about her religion, etc. Also a family friend who is a Christian who goes to church a lot BUT doesn't advertise on her car, etc judge people, etc is a great person and Christian. I have so many more examples in my life.

Why do low-key, humble Christians often feel more authentic than outspoken ones?
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