We already know that Tom Brady will be returning in 2018 for his 19th NFL season, which he'll play at age 41. Until late Friday night, however, we didn't know exactly why Brady was coming back for more. 

In an Instagram video seemingly taken somewhere along the California coast, we can see Brady working on his running skills.

The caption of the video reveals Brady's motivation for returning. It reads as follows: 

Ok so the main reason I'm still playing is I haven't hit 1,000 career rushing yards yet... 32 to go! #TB1K #CatchMeIfYouCan  #whereyouatAP #watchandlearnruss #cominforyouarodg #notsoeasyanymorevo n#qbsneakon3rdand1 😂🤷🏼‍♂️💯

Brady is indeed at 968 career rushing yards, at an average of 1.7 per carry. He needs 32 rushing yards to hit the 1,000 mark for his career, but getting there is no guarantee. He has failed to reach 32 rushing yards in a season in two of the last five years, including last year. 

No ad available

If he wants to catch Adrian Peterson (hence, whereyouatAP), at his current pace, Brady will need to play until he's around 226 years old. Brady has mused about wanting to play until he's 45 years old before, but as of this writing he only has wife-approved permission to play two more seasons. Something tells me Gisele is not going to approve of him playing for 18 more decades, so he's really going to have to pick up the pace if he wants to catch Russell Wilson (3,275 yards) and/or Aaron Rodgers (2,670 yards), let alone Peterson.