1) Going back to his college days he was routinely in the national championship hunt. And almost as routinely they would melt down against Oregon. Oregon was the big game they had to win but usually never did.
2) 2011 - 2012 season the 49ers have the NFC Championship game at home. They have a lead in the 4th quarter on their way to the Super Bowl. They come completely unhinged, fumble punts all over the place and lose the lead in the 4th and lose the game in OT. Mental errors are their downfall.
3) 2012 - 2103 49ers make it to the Super Bowl. They come out completely out of sorts and totally unprepared for the biggest game of their lives. They dig themselves a 6 - 28 deficit. The power goes out which causes a long delay. They dig their way almost all they way back. 2nd and goal at the 5 yard line and we call fade pass after fade pass to Crabtree in the closing minute. All incomplete and we lose the Super Bowl. The unprepared aspect at the beginning and the questionable calls at the end. The team didn't seem prepared.
You could argue the USC games in college. But IMO USC had already started their decline by that time and weren't as dominant. The "Big Game" in college in his conference would have been Oregon which he rarely won.
Harbaugh is no doubt better than we had. But can he win the BIG GAME under intense pressure?