Questions regarding 20% and 80% of threshold for deciding whether is a track mostly tracked or lost

[ykn96]

Hello, I was looking through the literature and i noticed that the thresholds of the definition makes use of 20% and 80%.
May i get a sensing of why are the thresholds these particular numbers?

mostly_tracked | Number of objects tracked for at least 80 percent of lifespan.
partially_tracked | Number of objects tracked between 20 and 80 percent of lifespan.
mostly_lost | Number of objects tracked less than 20 percent of lifespan.