This column originally was published on Real Money at 12 p.m. Friday.On Thursday, Apple ( AAPL) kissed $600 before pulling back -- and, all in all, since late November it's been a breathtaking move for a company this big. At that point, the stock had traded in the mid-$360s. I remember, at that time, there were many technicians on Twitter saying Apple's stock chart was broken and it was going to be an easy move down to $300. Well, here we are now at $600. It's remarkable. I've been long Apple for some time and had been complaining that the stock was underpriced. I was at an Apple Investor conference in Los Angeles this week, and many people there were touting the long-term potential for the stock, still, at these levels. I absolutely agree with their bullishness. However, after such a big move, it's very hard for me to be optimistic on the stock in the short term. In the last three years, every time Apple shares have hit a new round-number $100 level, it led to a big pullback and a consolidation before shares leapt above that level for good. We saw this happen at $200, $300 and $400. It's only been in these last few weeks, with the rapid move past $400 and $500, that we've seen the stock move so easily move through these psychologically important areas. Now we have new worrywarts saying a company this big can't keep growing at these levels. That's what they said when the stock passed $250 billion, by the way. We also have people saying Apple is a bubble because their grandmother has started talking about the stock, and because the stock's move has been so meteoric. As far as Apple's size is concerned, I agree with the bulls who say the company is in a far different situation than what's suggested by this, given its market-share levels in key markets and the potential growth of those markets overall. But I also believe those worrywarts: The achievement of $600 a share in such a swift period means Apple is in for a pullback. Friday, we'll hear about how well the new iPad sales are doing, and we'll hear about the first-weekend successes. Over the next two weeks, we're also likely to hear about sell-side analysts lifting upping their price targets on the company, reflecting sales of the new iPad. Yet, I just don't believe this can help Apple's stock for the next four to six months.