This necessity arises because the integrity of a transaction cannot be accurately verified without considering the entire transactional context, particularly when dealing with candidate header branches above certain milestones in the blockchain. The process becomes complicated as blocks above the one being validated can alter the status of previous outputs, affecting their existence and spentness within the UTXO store. Consequently, the sequence of transactions represented in the UTXO store is disrupted, undermining its reliability for script validation under these conditions.

The proposed solution involves assuming the validity of a branch above a milestone block, focusing efforts on populating the UTXO store up to that milestone. This approach, however, introduces significant challenges in maintaining thread safety and ensuring persistent locks across billions of outputs during search, comparison, and writing operations. These complexities highlight the substantial resources required to manage the UTXO store effectively under such a methodology.

To mitigate these challenges, an alternative has been implemented: downloading the full UTXO set based on the assumption of its accuracy. This method circumvents the need for intricate locking mechanisms and extensive data validation processes by leveraging a pre-validated dataset. Despite its potential efficiency gains, this approach underscores the trade-offs between computational resources and the integrity of transaction validation processes in blockchain systems.