Editting Roblox module execute err - lua

Question

-- This is some of the code made by Roblox themselves:
-- Setup table that we will return to scripts that require the ModuleScript.
local PlayerStatManager = {}
-- Table to hold all of the player information for the current session.
local sessionData = {}
-- Function the other scripts in our game can call to change a player's stats. This
-- function is stored in the returned table so external scripts can use it.
function PlayerStatManager:ChangeStat(player, statName, changeValue)
sessionData[player][statName] = sessionData[player][statName] + changeValue
end
-- Function to add player to the sessionData table.
local function setupPlayerData(player)
sessionData[player] = {Money = 0, Experience = 0}
end
-- Bind setupPlayerData to PlayerAdded to call it when player joins.
game.Players.PlayerAdded:connect(setupPlayerData)
-- Return the PlayerStatManager table to external scripts can access it.
return PlayerStatManager
--------------------------------------------------------------------------------
-- Require ModuleScript so we can change player stats
local PlayerStatManager = require(game.ServerStorage.PlayerStatManager)
-- After player joins we'll periodically give the player money and experience
game.Players.PlayerAdded:connect(function(player)
while wait(2) do
PlayerStatManager:ChangeStat(player, 'Money', 5)
PlayerStatManager:ChangeStat(player, 'Experience', 1)
end
end)
When I run these two script, it run perfectly, adding the print(sessionData[player][statName]) inside the ChangeStat function, but when I removed the game.Players.PlayerAdded:connect(setupPlayerData) part in the module script, it stopped working. I though module script does not execute code without it being called, and if that was the case, shouldn't the game.Players.PlayerAdded:connect(setupPlayerData) part be delay and not function since player's already added, therefore it not firing?

Answer 1

require executes the required code.
If that was not the case you would not be able to get a table through require, as your return PlayerStatManager statement would not be executed.
As a consequence removing
-- Bind setupPlayerData to PlayerAdded to call it when player joins.
game.Players.PlayerAdded:connect(setupPlayerData)
will cause an added player not to be initialized properly. This basically says: when a new player is added, call setupPlayerData.
Where setupPlayerData says: give a new set of stats to player
As you removed that line no player has stats. If you don't have stats you can't increase their values...
So obviously you did not understand what the code did befor you changed it. Therefor you cannot understand why your changes cause problems.
If you change a system you don't understand you can be lucky, but in most cases you will utterly fail.