Power shortage, or just a perceived shortage

Before David became king over all the tribes of Israel, he had only a small part of the nation under his control. Saul's son ruled the rest of it, assisted by Abner, the general of his father's army. But after a falling out, Abner defected to David's side. David met with him and Abner departed in peace. There was bad blood between Abner and Joab (David's general).

So Joab went to the king and said, "What have you done? Look, Abner came to you. Why did you let him go? Now he is gone!"

2 Samuel 3.24

I have often wondered why David didn't do something about this. Why didn't he say, "Don't mess with him - he's helping me unify the kingdom!" Or something. And after Joab killed Abner, shedding his blood "in peacetime as if in battle" (1 Kings 2.1), why didn't David do anything about it? Why did he wait nearly forty years to punish Joab? (As he was dying, David left instructions for his son Solomon to take care of business.)

I cannot figure it out. Although he says Joab and his brother are too strong for him, that just doesn't seem credible today, over 2500 years after the fact. Did he have a blind spot? Was he stuck with an outdated mental image of Joab and his brothers, an image formed in his mind years before?

It must be very difficult for heads of state (or corporations, or even large teams) to see beyond impressions from the past, to tell when their advisors aren't being objective (or honest), and so on. I can't even blithely say "Oh, he should have prayed more." This is David, writer of the psalms, the man after God's own heart!

Now that I think of it, parents are often blind to what's going on with their children. My kids have sometimes surprised me, and sometimes I've taken a position I wasn't sure I could. Sometimes I have more influence than I thought I had, if I just take the step of exercising it.