"I can't lie," Shanahan said on KNBR's Tolbert, Krueger & Brooks show. "When I told them we're going to run the ball 40 times, then I got up to my room later that night, I was like, 'What was I thinking? That's going to be so hard to do.'"
The Niners finished the game with 44 carries and routed their division rival 31-10.
Even if the team hadn't accomplished the goal, Shanahan was eventually glad that he set it. San Francisco had struggled on third down leading to the game. Against the Rams, the team converted eight of their 14 attempts.
"It was more of a mindset, and that's what I was really trying to do, not just for the team, but also for myself," Shanahan admitted. "I mean, you've got to have that mindset to do that and know that won't happen unless you do better on third down than you've done all year. And you do that good on defense, and you get the turnovers.
"So, we had that mindset, we did better on third down, and we got a couple of turnovers, and we didn't give the ball up. So, it all ended up equalling out to what the goal was. But I think it started with the mindset, and it carried over to third down. When you run the ball that well -- I like to say third down is its own deal -- but I think your whole team plays better when you run the ball like that."
That certainly appeared to be the case. The 49ers looked much-improved in every area, playing one of their most complete games over the past two seasons. In addition, the decision to include a heavy dose of the run game made the team look more like their 2019 counterparts.
"All of a sudden, you can block better because the guys aren't pass-rushing as much," Shanahan continued. "They've been defending so many things, and they're getting worn down, so you get a hair more time. I think the way our receivers competed, blocking -- if you just go back and watch [Brandon] Aiyuk, and Jauan Jennings, and Trent Sherfield, and Deebo [Samuel], you watch how they're blocking in that game, they're some of the most physical guys out there.
"I think when you play that way, it gets you so into the game that before you know it, you're running your routes better, you're attacking the ball better, just doing everything a lot more alert. I just think it carried over to everything."
The 49ers hope to carry their momentum into Week 11 when they travel to TIAA Bank Field to play the Jacksonville Jaguars.
You can listen to the entire conversation with Shanahan below.