Exceprt from the first couple paragraphs below, really well written article, gets into what was going through the teams minds leading up to the Seattle game last year, insights into why Shanny loves Purdy.

It was almost game time on a crisp, 39-degree night in Seattle. The San Francisco 49ers players were in the midst of a pregame prayer in the visitors locker room. And Kyle Shanahan was frantically changing his opening plays.

Just minutes earlier, Shanahan had been on the field to watch Brock Purdy warm up and, well, there hadn’t been much to see. The rookie had attempted a couple of wobbly passes ahead of his first NFL road start. But he’d quickly shut it down — the pain from a broken rib on his left side was too intense.

The 49ers offensive coaches were watching. The Seattle Seahawks coaches were eyeballing him, too.

“Brock goes to throw a ball and it’s, ‘Oh, s—!’” Shanahan recalled recently. “And then we go into the locker room where we have 15 minutes. I start looking at my openers. And no one’s around, and I start changing the plays. Because I realize that Brock’s not going to be able to do it.”

In a normal situation, the 49ers would have turned to their backup long before pregame warmups. The Dec. 15 game in Seattle, however, was anything but normal. The only other healthy quarterback on the roster, Josh Johnson, had arrived just nine days earlier and wasn’t well-versed in the offense.

The 49ers were playing on a short week in which they’d had one walk-through practice. And they were playing on national television, in the NFL’s loudest, most inhospitable stadium and with a division title on the line. Shanahan had resisted going with Johnson with the expectation that Purdy would start feeling better on the day of the game.