As a buy and hold investor, you're in it for the long haul: you're going to hold onto your investment for as long as possible, and if it dips, you'll be there to buy more. As a trader, you're trying to make money by buying low and selling high—and hoping that when you sell high, someone else will buy low.
Also, as a buy and hold investor, you'll probably have a better chance of seeing your investment grow over time. And if things go south? Well… that's not good news for anyone who isn't prepared for it. Traders can take advantage of market volatility (that is, when prices swing up and down), but they run the risk of being caught flat-footed when things go south—and then getting stuck in an even worse position than they were before.
In short: if you want to play it safe, go with buy and hold. If risk-taking is your middle name (or at least one of them), then maybe trading is right for you.