I give you Barack Obama circa 2007. Hillary Clinton was running (or at least everyone knew she was running) and the conventional wisdom directed at Obama went something like this: "You're a young guy with a bright future. Why not wait an election or two to run in your own right? You could help unify voters behind Clinton and give the party its best chance of winning in 2008."
Obama, of course, didn't follow that advice. He saw a path right then that would get him elected to the top job, not Clinton. He took lots and lots of flak for it. He's too young! Wait your turn! It's bad for the party! Also, he won. Selfish decision — and a very smart one.
Fast-forward to Ryan. The truth that Romney speaks — albeit it in a circuitous way — is that the path to the speakership and the path to the presidency are not the same path. (If you bet the "over" on the number of times I would write "path" in that last sentence, you won!) The last speaker of the House to be elected president was James K. Polk — way back in 1844! Before Obama, the last sitting senator to be directly elected to the White House was John F. Kennedy in 1960. And with Republican primary voters growing increasingly disenchanted with Washington and everyone in it, volunteering to be the face of Washington Republicans isn't exactly the best career choice if you do want to be president.
The simple fact is that if Ryan does want to run for and/or be president one day, becoming speaker is a very bad idea. Ryan has been rightly selfish before — turning down repeated overtures to run for Senate or for governor over the years. (With Ryan as the GOP nominee in 2012, is it possible he beats Sen. Tammy Baldwin to hold the seat for the GOP? Sure.)
When the House returns to Washington this week, Ryan will be under intense pressure to pick up the speaker's mantle for the "good of the party." If he still harbors the dream of being president, he'd be well advised to listen to his friend Mitt Romney. He's a cool dude. He's trying to help you out.