Anything can happen in one individual game of baseball. Anything can happen in a few games of baseball. Heck, anything can happen in a course of a few weeks of baseball. It’s a marathon sport where the long game is the only game you can reasonably play while still saying sane.
That’s because there’s a lot of noise in an individual game of baseball and not a lot of signal. It takes a lot of games for there to be more signal than noise, and the previous season’s results are usually more indicative of true talent—both at a team level and on an individual level—significantly far into the season.