Ok if you wnat me to continue on with that and make it more practical.
If you dont trust anyone and have gone to the extreme then that can do you harm. You meet a new girl but seem extremely untrusting. Not good for you as you constantly think people will let you down and that creates stress. You then change your behaviour and instead of getting on as a happy chap with your new girl she notices you are stressed, closed off and feels uncomfy about it. That makes you less attractive as a friend/bf as she wants someone who trusts her (especially if she's done nothing wrong) and she can trust in return. Mistrust can protect you, but overdo it and it damages. Caution is fine.