Mike Flores's article Who's the Beatdown, despite its brevity, is perhaps the most influential piece of Magic theory ever written. The idea of playing your aggressive deck as a control deck and vice-versa as a way to get an edge in a matchup where your plan A is outclassed was novel twenty years ago, but has since become commonplace, leading to today's huge emphasis on versatility in sideboarding.
Our understanding of Magic has also progressed to the point where we often talk about shifting roles within a single game. In a typical control or midrange versus aggro match the bigger deck takes on a controlling role early, but often wants to turn the corner quickly and shift roles into the aggressor once they run their opponent out of resources so the opponent doesn't have an opportunity to draw a threat that forces another answer.
Where things get interesting is in a control mirror. Both decks want to play a long game and are filled with cheap removal to answer early threats from more creature-heavy decks, but those cards aren't good against another answer-heavy, threat-light deck. This naturally leads to very long games that are centered around a few critical cards.
After playing recently with Blue Moon in Modern, I've gained a solid grasp of the dynamics at play in evaluating the game state in a control mirror and positioning yourself into the proper role.