Every new innovation is the result of an attempt to solve a problem. Blockchain technology is no exception. It's quite evident after learning about the evolution of blockchain technology that it arose because of a need to address the inevitability of uncertainty in the existing economy.
Uncertainty could never be eliminated, but only lowered: there have always been institutions that have acted as third-party lawmakers to lower uncertainty, or lack of trust, whenever there was a need for an agreement between parties. A typical example would be buying an item on eBay. You would always need as much certainty as possible about the trade. One party expects fair goods, and the other expects agreed money. Now, though the buyer and seller have no reason to trust each other, they complete their trade as they trust the third party, which is eBay, who assures them both of a legitimate trade. Again, there was a need to trust these "medium" institutions. Trusting an institution requires a lot of research and knowledge. Blockchain promised to overcome these issues by implementing applications in a decentralized and secure way, assuring some level of certainty. This was one of the main reasons behind the widespread adoption of blockchain in a trustless society.
We know that blockchain is an ideal technology for implementation in trustless environments. However, the blockchain alone is not responsible for the success of the complete implementation. It's assisted by several other protocols that make it the robust and resilient technology it is. Blockchain can be implemented in trustless networks mainly due to the decentralization of computation in dense P2P networks and the maintenance of a secure and publicly distributed ledger that gives complete transparency over the entire blockchain. The P2P protocol makes sure that every node holds the latest state of the blockchain.
The need for decentralization is the key motivation behind the blockchain technology, and decentralization is achieved by distributing the computation tasks to all the nodes of the blockchain network. Decentralization solves several problems of traditional systems; the single point of failure is one such problem. For example, in a centralized system such as a bank, the user would always communicate with the same third-party bank to fetch their account details. Although this transaction may be possible almost every time, 100% uptime is not guaranteed, as this server is centralized and has just a few backup servers for load balancing. There could well be a situation where all the servers could be flooded with requests, resulting in crashes and server shutdown. This downtime is something that's inevitable, even in perfectly architected servers. If the same scenario was faced in a decentralized network, it wouldn't be an issue, because all the transaction data would be distributed across all the nodes, meaning that each node can act as a backup node in case of failure, maintaining the integrity of the data (another key benefit of blockchain-based solutions). This is something that's achieved by maintaining a distributed ledger of blockchain data. Blockchain immutability, which is a key factor in trusting the integrity of the blockchain, ensures the integrity of the ledger, which is publicly accessible to all nodes.