It's not really anger. It's more of a chronic and intense frustration, now turned into nothing more than a dull, incorrigible ache thanks to its continuity.

But she can't tell the difference.

It's not difficult to understand her frustration. She's not talented like Sasuke and she doesn't carry a burden like Naruto. It's true that Naruto is often less capable than her during their missions, but his abilities tend to rapidly fluctuate, depending.

At her best, Sakura is mediocre, and Sakura is always at her best.

It's not anger. Anger breeds passion. And for this, she almost wishes it was.