This is more of a question, rather than an idea.
Most of the time, people actually disappoint you, if you are any ambitious, a perfectionist or have high expectations for yourself and humanity.
On the other hand, research indicates that people who trust others on average have a higher life-expectancy.
One idea I had was:
Often, contradictory beliefs can be beneficial. Perhaps, you can sometimes believe that others are not to be trusted. For example, when you want something to be done correctly/the right way. On the other hand, when it’s not important to you or anybody else, you might just believe that people are to be trusted. In other words: don’t have high expectations when you care about something. Believe that it will go wrong and accustom yourself to appending disappointment.
It’s more likely that your expectations and hopes won’t be disappointed for small things. E.g. if you have an appointment with somebody for a non-work call, it’s unlikely that they will disappoint you. Generally, it makes sense to believe that people won’t disappoint you here.
For bigger things, you generally believe that people will disappoint you, since they are less likely to uphold your agreement.