Blockchain systems and especially public and distributed ledgers are often called "trust mechanisms", "trust networks" or "trustless systems". All these labels refer to the same idea, distributed and transparent nature of a network system. A bold promise of blockchain is said to be a system that removes the need of trust towards any single entity. For example, in its ideal form (excluding intermediate trading platforms), bitcoin transactions do not rely on trustworthiness of any specific intermediary. Instead, there is a whole network that consists of distributed nodes that validate and confirm transactions. As a result, received bitcoins are real within the protocol and not counterfeited. There is no threat that a single node could capture and keep the bitcoins for itself either like in the case of a physical gold transportation. However, this does not mean that a system would completely or even essentially supplement the need of all kinds of trust. Distributed ledger system merely changes the object of trust. In search of a balanced view it must be admitted that while trust technologies have potential to reduce certain uncertainties, their complex nature also introduces new kinds of uncertainties.
First, we need to give "trust" a sensible definition. There exists a wide range of literature concerning trust with certain differences in definitions. Essentially, trust is a subjective perception. Probably the first thing that trust may bring in mind is goodwill. Trust describes person's willingness and effort to fulfill liabilities to others. A trusted person may still fail fulfilling expectations despite honest intentions and effort. That is, trustworthiness also depends on sufficient abilities. So called "competence trust" describes this necessary element. In any case both goodwill and competence trust are about expectations of behavior or functionality in an uncertain future. In everyday language trust often refers to predictability and reduction of uncertainties. Especially competence trust and systemic predictability are close and even overlapping terms. Abilities or competence can be about humans or technical systems designed by people. Furthermore, experiences and "objective" credentials shape perception of trust. Often an individual or a group of people may serve as the first hand object of trust between trust towards another person or technology.
Being aware of competence trust and its proximity to systemic predictability, many different trust issues can be identified concerning bitcoin and other blockchain systems. First, the use of a blockchain system implies trust towards durability of a network and belif in it behind the actual technical system. Another focal issue is trust towards the technology, competence of the people behind design. Does the system work at all? Can there exist errors or vulnerabilities in the code that may cause problems in the future? Does the technology impose limits for its efficient utilization in the future? Errors or other technical limitations can be fatal for distributed networks whose coordination and correction happen inefficiently (as the Bitcoin SegWit debate last year has shown us). Technical limitations are also intertwined with goodwill issues. Loopholes make a system appear as an easy target for abuse even among the network that was originally trusted (e.g. "fork attacks").
Another trust issue about the network is slightly a game theoretical one. Sometimes the use of a network requires fixed costs and commitment, whereas its value comes from other people owning or using the same network. For example, existence and behavior of major bitcoin owners imply that the system preserves its value and even increases it. They believe that other people are using bitcoins or at least having similar expectations of the same underlying asset. This game theoretical shared belief aspect does not exactly fall into the category of goodwill, but nevertheless constructs a necessary element to overcome uncertainties. In sum, a technology that can significantly reduce uncertainties related to goodwill trust introduces new kinds of uncertainties and need for trust. They need to be assessed and potentially managed in order to decide, whether any trust technology can cut the total perceived uncertainties.