If I lose this game what do I lose in life? Time.
FTFY.
Sometimes you also lose money.
Anyway, the issue at hand here is a wee bit more complex than just "it's a game". You get mad because your mouse is shit, or Windows updates decides to bug you about a restart when that boss you've been grinding on for half an hour is at 5% HP, or internet connection goes poof, or game crashes. In MMOs, you rage at horrible RNG or evidence of class imbalance, or in some cases it's simply lack of fairness from game mechanics.
It's not really about losing a game; it's about losing a game due to specific causes and/or for the umpteenth time. The frustration level builds up, and most times the root cause is the game itself: the way it's designed or coded.