system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:  Why did we evolve our tails away?

As an outdoorsman, I feel like it would be so beneficial.  I could balance better when wading across slippery rocks and crossing logs, and I could smack away flies when I've forgotten my DEET.  In everyday life it would be pretty cool too.
gpt
Quadrapeds (four legs) use their tails for balance when walking, and as a rudder to stear while running at high speeds. Bipeds (two legs, two arms) like monkeys use their tails for balance as well as an extra gripper while climbing. Upright Bipeds (only walks on two legs) have a totally different balance to maintain; if we had tails, we would need to have them between our legs to keep from falling backwards. A tail that would maintain balance in an Upright Biped would be so short that it would not be useful for your needs, being maybe half a foot long.