For one thing, people can build trust with the intend to abuse it after a longer period of time. An abuser, for example, could plan to offer 20 "good rides" on Uber until s/he strikes. For another thing, many people have learnt to skillfully simulate trust which may pose a problem for you. For instance, you may believe to be in a loving relationship but all of a sudden you find out that the other person isn't interested in you at all and just didn't want to be alone etc.
The book "Phishing for Phools" has a good chapter on "reputation mining", which is essentially that, with the added wrinkle that you can buy a company that has a good reputation and cut corners until the customers wise up. I'm looking at you, InBev.
For one thing, people can build trust with the intend to abuse it after a longer period of time. An abuser, for example, could plan to offer 20 "good rides" on Uber until s/he strikes. For another thing, many people have learnt to skillfully simulate trust which may pose a problem for you. For instance, you may believe to be in a loving relationship but all of a sudden you find out that the other person isn't interested in you at all and just didn't want to be alone etc.