Very often we encounter a situation where a customer would like to implement an additional level of security in the form of a SIEM solution, but cannot yet specify their requirements. In this case, they then choose a "box" solution, where the supplier delivers a box, some logs are directed to the system and 200 security rules are enabled, and the system does something. And here is the primary stumbling block. Just because the system is green doesn't mean it is doing what it is supposed to do, or even doing anything at all.
Further, security must not end with the implementation of the SIEM tool, but must continue with other processes such as defining playbooks for the SOC team's needs, defining test scenarios by which the system must be tested regularly, and other activities for the proper functioning of the SOC team.