There will often be times when it is wise to take a backseat, to keep your head down and not get involved. Some situations are best avoided, as the hassle of getting involved far outweighs any potential benefits. But, there will also be times where we are tempted to bow out, to slip quietly away and leave it to other people to sort things out when perhaps that is not the wisest strategy.
For example, there will be times when someone is being treated unfairly or in a way that undermines their dignity (bullying clearly comes into this category). We may be tempted to stand back and pretend we haven’t noticed. However, much of such bullying (and other forms of unacceptable behaviour) flourishes precisely because people do not challenge it.