Despair is that feeling that you are too sinful for God to forgive you, and then you choose to die without accepting God's salvation. It's an unforgivable sin because because the person who has this mindset dies unforgiven because of choosing not to not accept God's gift of salvation.
I don't want to get into a discussion of religion. I'll gladly discuss the Bible with anyone anytime but too many people are very loyal to their religions and I don't want to offend anyone even if unintentional.
Knitting I can understand why some would believe what you've explained.