He explains progress between teammates as two intersecting sinewaves that ramp up together. Both of you plateau at different times, and peak at different times.
|You're the green, your teamate is the red|
I love this example/analogue as it sums up those times when I easily tap out my teammate one week, only to be smashed the next week.
I think the moral of what jack was trying to say is that regardless of the short term "ups and downs", when you look at it on a longer timeline it is easy to see the upward trend of both of you.