CAPM Practice: Determine how to follow and execute planned strategies or frameworks

Alexei Iyer is managing a software development project at Quasar Media. During a risk review meeting, the team identifies that a key vendor may not deliver components on time. The risk management plan specifies documenting risks in the risk register and assigning owners. However, Alexei believes this risk is minor and decides to skip documentation. Three weeks later, the vendor delays delivery, causing the project to miss a milestone. What was Alexei's PRIMARY mistake?