When is the last time you trusted someone with something that is truly important to you? Wether it is information or an object you value, I am sure you put a great deal of throught into the matter. Trusting someone with something important is like taking a part of your life, loaning it away, and hoping it returns in one piece. If it does, we oftentimes get something additional in return in form of an important insight or comforting words. If, however, your trust is misplaced, the consequences may be dire.
Trust is, in a way, a gamble. What's so special about it, however, is that the value of bets is not universal, but it alters between players. Take, for example, a teenage girl who is infatuated with some boy and decides to take a chance and tell him how she feels. Or in other words, trust him with personal information she holds in value. Now, depending on the boy's preposition towards the girl, he can view the girl's advances in low or high value and respond by giving back something he considers to be of an equal value. If the boy likes the girl, he could suggest a date, returning the girl's trust with his time and intimacy. On the other hand, if the boy despises the girl, and thereby holds the trust she placed on him in a lower value, he could ridicule her for her feelings or look for personal gain.
This is why people build their trust on anothers, instead of trusting them right away. Because people and their values and prepositions towards eachothers are different, at first it is better to trust others with things you don't hold in a great value and thereby don't fear losing so greatly. If the person responds with near-equal trust, you can feel more comfortable to trust him with something greater the next time. As this cycle continues, the level of trust will set in an equilibrium where both subjects feel they don't want to share more valued things with eachothers.
The system also has an interesting flaw in the existence of a possibility for a scenario where a person trusts another with something that he holds in a low value and the another in a high value. This will create a massive bias that has the potential to be extremely uncomfortable for the first person and extremely confusing for the another, and even prevent further interaction between these two persons, preventing the correction of their trust-levels.
On an unrelated note, if there is some matter that you would like to have me think about, feel free to suggest it in the comment section of this post. If I find it interesting, there's a good chance I'll write about it.