Goku had his first bout with Goku Black on the English language broadcast of Dragon Ball Super, and while the fight was a great first taste at what is to come, neither of the fighters were close to using their full power.
In fact, Goku's biggest flaw as a fighter is highlighted here. As Vegeta points out, Goku has a bad habit of not using his full power during fights until he feels the situation calls for it.
Goku being battle hungry has been a staple of the series for the entirety of its run, and this is only the most recent example of how his low-balling a foe could lead to a more disastrous outcome. When he played around with Majin Buu as Super Saiyan 3 in the Majin Buu saga, his failing to deal a fatal blow is what causes Buu to run rampant throughout the rest of the saga.
It's very much the same case with Goku Black. Goku doesn't take the battle seriously, as he finds himself testing his power against himself rather than seriously taking on a foe Future Trunks is frightened of. And because of it, the ramifications are already severe.
Not only did Goku Black destroy Trunks' time machine before being forced back to his time, in the next episode preview the almost playful fight with Goku seems to be improving Black's fighting proficiency as well.
Goku usually messes around before he takes a fight seriously, but now he's facing a foe with the same ability to quickly get stronger as he does. If Goku does not fix this flaw any time soon, Black will only get more dangerous since he's going to be far less playful.
DragonBall Super airs on Crunchyroll Saturday evenings at 7:15 p.m. CST. Adult Swim airs the English dub during its Toonami block Saturday evenings at 9:30 p.m, and is now available to stream on FunimationNOW and Amazon Video.
If you want to catch up with the English dub, the first 39 episodes of Dragon Ball Super are now available to stream on FunimationNOW, Crunchyroll's VRV service, and available to purchase on Amazon Video. The 39 episodes span the full range of what has aired in the North America and covers the "Battle of Gods" arc, "Revival of F" arc, and the most recently ended "Universe 6" arc.
Funimation has previously announced the rest of the series will soon be available on the service as well. Releasing in 13 episode batches two weeks after the last episode airs on Cartoon Network, fans of Dragon Ball Super's English dub without a cable connection will soon have a way to experience the series.
There is also currently a new Dragon Ball film in the works for 2018. The film will focus on the Saiyans, the "origins of Goku's power," and potentially the story of the very first Super Saiyan God. Not only does it aim to be the best film in the series, original creator Akira Toriyama will be contributing to the film's script and new character designs.