Agassi wasn't loud-mouthed to be exact. Agassi was on a journey of self-discovery, and wasn't sure who he was. He resented playing tennis (until much later in his career), and disliked authority. The combination of these factors came out as someone who was 'badass'.
Sampras was single-minded in his focus for achieving greatness, but he wasn't always that way. It took a defeat on the tennis court in his early twenties to give him the pure appetite for winning. Before that, he was ok with losing.
Sampras ended his career earlier for a few reasons; spending more time with his family, feeling he had nothing left to prove, and the emergence of Roger Federer!
Agassi clearly found a resurgence in his tennis once he hated it less, and having his premier rival no longer around to stop him winning Grand Slams, felt he could still achieve more.
Sampras was single-minded in his focus for achieving greatness, but he wasn't always that way. It took a defeat on the tennis court in his early twenties to give him the pure appetite for winning. Before that, he was ok with losing.
Sampras ended his career earlier for a few reasons; spending more time with his family, feeling he had nothing left to prove, and the emergence of Roger Federer!
Agassi clearly found a resurgence in his tennis once he hated it less, and having his premier rival no longer around to stop him winning Grand Slams, felt he could still achieve more.