It’s really good that Oikawa has Iwa-chan to put him in his place.
With Oikawa’s pompous attitude and foolish actions such as pushing himself too hard, Iwaizumi knows Oikawa better than anyone since they are childhood best friends, and knows how to handle him best.
Oikawa needs Iwaizumi to be stable, and Iwaizumi needs Oikawa to keep himself going. There’s honestly no better match or person that can keep Oikawa in line and confident other than Iwa-chan. The only person he ever listens to is Iwaizumi.
They both simply compliment each other perfectly. (ಠ_ಠ) ♡ (○ﾟε＾○)v♪