"I didn't look into him, obviously, as much as I should have," the 49ers coach said during Tuesday's Super Bowl LIV media session at the Hyatt Regency in Miami.
Reporters laughed as Shanahan went on to explain why the reigning MVP, whom he'll face Sunday when the 49ers play the Chiefs, didn't have his full attention three years ago.
If you need a two-word summary of that explanation, here it is:
Kirk Cousins.
"I think it's well documented the relationship I had with Kirk and being in Washington and everything," Shanahan said. "I felt very confident that he wasn't going to stay there [beyond 2017]. So anytime you go into a season knowing that a franchise quarterback is going to be available the next year, it made me a lot more picky for what we were looking at."
The 49ers had the second pick. They traded it to Chicago, moving down to take underachieving pass rusher Solomon Thomas after the Bears whiffed on Mitch Trubisky.
Seven picks later, Reid and the Chiefs pounced, moving up from No. 27 while throwing in a third-round pick and a first-rounder the next year.
"We definitely looked into [Mahomes] and studied all his tape," said Shanahan, who also interviewed Mahomes at the combine. "He was just a freak. He could make any throw. Had the ability to do anything."
But he was far from being considered a guy who would become the league's best player in his second season. At the time, there were concerns about horrible footwork and being a produce of Texas Tech's "Air Raid" system.
"We did not feel like from all the intel you get and stuff that he was going to go that high," Shanahan said. "It's very tough when you watch college systems and you don't really know until you get someone in the building. You can see the ability, you can see talent. But how's the mind? How do they play in the pocket? How do they process? That's not just an IQ score. I don't think that's something you can totally test. You have to go through that with them.
"So there's always a risk with that when you spend a first-round pick on a quarterback. And the situation we were in, we didn't want to be that risky, especially with the second pick in the draft."
Shanahan's plans to swoop up Cousins were derailed when the Patriots called and offered Jimmy Garoppolo for a second-round pick at the trade deadline in October of 2017. Shanahan was 0-8 as a head coach at the time.
"The trade offer just randomly came out," Shanahan said. "The last time we had talked about it was down at the combine, and we definitely got a no to it. It came out on a Monday that we found out. About 30 minutes later, he was on our team."
Bye-bye, Kirk. Cousins signed with the Vikings, who were quietly dismissed by the 49ers in the divisional round this year.
Speaking of that game, Shanahan drew some more laughter when asked what he learned from being Atlanta's offensive coordinator when the Falcons blew a 28-3 third-quarter lead in losing to the Patriots three years ago.
After saying his only regret was calling a pass play that led to a key sack on second-and-11, Shanahan admitted that he's still got some leftover scars from that loss.
"You can never relax no matter what situations I've been in since then," he said. "You can ask our players. You can ask our coaches. I freaked out at [defensive coordinator Robert] Saleh when he tried to take the starters out against Minnesota when we were up like three scores with two minutes to go.
"I freaked out. But then I did the math and felt it was all right."
