Essentially, a hard fork makes the older version of the blockchain protocol invalid. In case the older version keeps running, they will end up with a different protocol and data as compared to the newer version. It can lead to possible errors and confusion. On the other hand, a soft fork is the opposite of a hard fork, where the new changes are backward-compatible with the older protocol. Hard forks can be risky, and potentially messy, and they spark double-spending. Soft forks don’t carry the risk of double-spending.