One of the most common questions is the difference between the red and blue teams. People are also confused about why there are two teams in cybersecurity and can one replace the other? In short, there are two teams by standing on two perspectives in cybersecurity, and we need them both.
The blue team stands on the defender's side, in which the team focuses on visibility, context, and control. On the other hand, the red team is on the attacker's point to test the strength of points in defense. For example, the blue team likes the combination of security in the world. We have immigration officers who check visa and passport, polices who make sure everyday safety, campus and building securities where we need a higher level of security, and bodyguards for VIPs. All these are in the blue team's responsibility which protects both breadth and depth. The red team then try to forge a visa/passport or fingerprinters, trespass into security zones, find logic flaws in management and workflows, etc. Its goal is to test the defence of their limits and break them so that the teams can work together and find a better solution. I think so far it is easy to see the difference with the real world analog.
In short, the blue team needs a wide range of knowledge, and the red team needs a deep and relatively narrow knowledge to push some points further. Also, the red team's tests often after the blue team's new solution, in which way build up a healthy circle to extend the depth and width of defense.