We tend to think of a baseball team as 25 guys. A group that hardly changes from Opening Day to securing a World Series championship seven months later.

In reality, we find four dissimilar stages for the modern World Series contender. Which tends to leave fans discombobulated and ticket-purchasers angry.

This is how “one team” wins a World Series in four phases.

Part 1: April 1 to August 1.

This is the team you, the fan, think you know. The 25 guys who came out of spring training, ready to make a run to the playoffs.

Key characteristics include a starting rotation that goes five deep and, given the steady rise of pitchers in the bullpen and consequent decline in non-pitchers on the bench, at least two guys on a very thin bench who can play multiple positions in the infield or outfield, or both.

This team is out there day in and day out for about 100 games of the 162-game regular season.

Then, often, it suddenly undergoes significant changes. The 100-Game Team exists not to win in October … but to get the club within sight of the playoffs.

The key moments come at the end of July, when the 30 Major League clubs make a decision on whether they are good enough to continue a playoffs push. If so, they look to make trades ahead of the non-waiver trade deadline of August 1. If they consider themselves doomed, they are the teams who send key veterans and guys with large contracts to the contenders.

This often makes for a batch of dramatic and, to some fans, traumatic changes. (In New York, for example, the Mets doubled down on their pennant push, while the proud Yankees threw in the towel.)

Part 2:  August 1 to August 31.

This is a month, about 30 games, in which the “buyers” in the days up to the August 1 non-waiver trade deadline try to demonstrate they have made the changes that keep them on course for the playoffs. Most of those teams will be looking at trading for veterans (in this case, players like Jay Bruce, Carlos Beltran, Jonathan Lucroy, Aroldis Chapman) to make them better. Meanwhile, the “sellers” at the trade deadline essentially quit on the season, offload some of their expensive veterans and give playing time to prospects — which may leave ticker holders for this time of year less than happy. Your team of April-May-June-July may have undergone significant changes, so buy a scorecard.

Part 3. September 1 to the end of the regular season.

Teams undergo another transformation, this time exploding from a roster of 25 to as many as 40. This is four-plus weeks of a form of baseball not played in the first five months, one with an extra 15 players hanging around, leading to all kinds of situational substitutions of both pitchers and hitters — because managers don’t have to worry about running out of players or how long their team’s boxscores become. In recent times, some teams have added a player who amounts to a “designated runner” (see: Terrance Gore) — who may not be able to field or hit, but in September that doesn’t matter because managers have enough players to have one who does almost nothing but steal bases. The one month of the seven in the season in which this happens.

Part 4. Basically, the month of October.

This is the playoffs and, eventually, World Series, and requires yet another sort of baseball team. For one, the manager is back to 25 players. And remember that five-man rotation you really needed in the regular season? That’s so over. If you have four starters, that’s plenty, in the playoffs, with all the travel days jammed in there. Actually, you almost certainly can get away with three starting pitchers. Which could mean a smaller pitching staff and one extra position player. Managers don’t worry about resting position players and also are inclined to let their top pitchers throw more pitches, and appear in relief. (See: Madison Bumgarner, 2014 World Series).

So, four distinct teams for each MLB club that gets to the playoffs. The guys there on Opening Day, whoever joins in the upheaval of late July, the 40-man club of September, and the ace/star-oriented group that plays in the postseason. And to win a championship, your team pretty much needs to be good in all four parts of the season.

So, if you have trouble keeping track of your team, you are not alone. This is a sports case of split personalities writ large. The guys splashing bubbly after the World Series … may include lots of faces that were nowhere in sight on Opening Day.