Given the way a blockchain functions, it is clear that blockchains can enhance trust by providing a mechanism to prevent opportunistic behaviour in an adversarial environment. There is, however, a limit to what a blockchain can do regarding trust. Although a blockchain can ensure the ledger is tamper-proof, there is no implicit guarantee that what is stored in that ledger is correct. For example, if the blockchain is fed false data with no mechanisms in place to check the validity of that input, the false data will be stored as truth. While users may provide false data attempting to manipulate outcomes to their benefit, false data may just as well arise from erroneous data imported from other IT systems, malfunctioning sensors, or human error.
There is also the risk that the people behind the blockchain are either acting maliciously or making errors, potentially making the entire blockchain system untrustworthy to its users. This risk is one of the reasons why blockchain operators often publish the source code of their blockchain software. This allows anyone to test the trustworthiness and correct functioning of the software. While only experts can do such an analysis, transparency is known to build trust.
Finally, there are threats to the functioning of the blockchain to consider. In public blockchains a single party can gain control over more than half of all nodes, allowing that party to manipulate the consensus algorithm to have favourable outcomes. But achieving this level of control may be practically impossible or at least very difficult for blockchains with large communities. There is also the already mentioned risk of false data being stored in the blockchain, possibly invalidating all future usage and processing of that data. This poses a major problem regarding trust for all types of blockchain systems and the business models these blockchains support: from blockchains that execute financial transactions to those that are used to verify the origin of products in support of international trade or sustainability programmes. False information can lead to losses, unfavourable outcomes, and ultimately loss of trust.