Lincoln Riley addressed his decision to leave Oklahoma and become the head coach at USC, calling it "probably the most difficult decision of my life."

Riley added that he accepted the Trojans' offer "based on my willingness to go take on a new challenge, and I felt like it was the right opportunity for me and my family to do that."

USC also shared a statement from Riley:

USC is planning to hold a press conference Monday at 6 p.m. ET, which will potentially see Riley face pointed questions asking for more insight into his thinking.

This move isn't necessarily unparalleled, but rarely does a head coach leave what Riley had in Norman, Oklahoma, for any other position at the college level.

The Sooners have been one of the most consistently successful programs in the country. 

They won 12 games in each of Riley's first three seasons and qualified for the College Football Playoff in 2018 and 2019. Before the 38-year-old arrived, Oklahoma failed to reach 10 wins just four times in Bob Stoops' 18 years at the sideline.

While Norman isn't the biggest draw in terms of recruiting, Riley basically had everything a coach could ask for. When he said he was "not going to be the next head coach at LSU" after OU's loss to Oklahoma State on Saturday, that seemed to be the final word on the matter.

Instead, the Texas native is leaving Oklahoma behind for what is effectively a rebuilding job at USC. The Trojans stagnated under Clay Helton, and they're likely at least two years away from being a serious national power again.

The one question on everybody's mind—and surely something he will be asked about on Monday—is how much the Sooners' eventual move to SEC motivated his decision.

Perhaps Oklahoma will continue to be a perennial playoff contender when it begins playing an SEC schedule, but the road to CFP will undoubtedly be more difficult. USC provides Riley with a more clear path if he can succeed where Helton failed in terms of bringing the best in-state talent to Los Angeles.

The Trojans might also provide more job security given how quickly things unraveled for Ed Orgeron and Dan Mullen at LSU and Florida, respectively.

Oklahoma is in a far better overall position, but it only needs to look to Nebraska to see how aligning with a more competitive conference and abandoning geographic rivalries can backfire in a big way.