We go up as long as the easy money keeps coming, or maybe it stops for "sell in May".
As soon as something triggers people and funds to reduce debt levels, the markets will turn south. You have both the "carry trade" money, Private Equity debt financed buyouts, and record margin debt from hedge funds and retail all out there pushing the market higher. Take some of that away and there is a problem.
Example: When the yen went up, we had a 500 point down day because the funds borrowing yen to invest in world wide markets didn't want to need to pay back more expensive yen, so they sold whatever they could, including even gold to reduce debt. IMO, if the yen were to start getting stronger again, the funds having seen that relationship last time will sell to reduce debt sooner next time to avoid having to sell at a lower price later.
Note, I'm not short, nor am I predicting a big correction will occur Monday or anything, just saying I think when it does happen, I think it will be caused by something that reduces debt and liquidity like that.