When you press "Find match", the game is not picking opponents at random. Behind the scenes it keeps a hidden number for you, usually called a skill rating or MMR (matchmaking rating). Every player has one. A higher number means the game thinks you are more likely to win.
The matchmaker's job is simple to say and hard to do: put you in a match where the result is genuinely uncertain. If you win nearly every game, you are bored. If you lose nearly every game, you quit. Games that feel fair tend to be the ones where each side had roughly a 50% chance.
The classic version is the Elo system, invented by Arpad Elo for chess. Its core idea is a prediction: the bigger the gap between two ratings, the more likely the higher-rated player is to win. If two players have the same rating, the prediction is 50/50. A gap of 100 points gives the stronger player about a 64% chance, 200 points about 76%, and 400 points about 91%.
After the match, both ratings move. The size of the move depends on how surprised the system was. Beat someone far above you and you gain a lot. Beat someone far below you and you gain almost nothing, because that result was expected. Lose to a much weaker player and you drop a lot.
Set your rating and your opponent's rating, then play a match. Watch how the same win or loss moves your number by very different amounts depending on who you faced.
Your rating changes only when a match is played. Rating shown above is the starting point.
Try three things. First, set the opponent 400 points above you and force a win: you gain almost the full 32 points. Second, set the opponent 400 below you and force a win: you gain about 3. Third, keep both equal and play 20 matches: your line wanders up and down by luck alone, which is why a handful of games says little about skill.
Plain Elo is the starting point, not what most modern games use. Real matchmakers usually add several things:
Uncertainty. A brand-new player has an unknown skill, so systems such as Glicko and Microsoft's TrueSkill track both a rating and how sure they are about it. New accounts move fast at first, then settle down.
Teams. In a 5v5 game the system compares team strength, often built from each player's rating, rather than one person against one person.
Speed and connection. The perfect opponent may be on another continent or take ten minutes to find. Most games loosen the rating match the longer you wait, and prefer players with a low ping so the game plays smoothly. A slightly uneven match with good connection often beats a perfect match that lags.
Hidden or visible numbers. Many games hide the real rating and show you a rank, tier or badge instead. Those labels are usually bands of the underlying number, and some games keep separate hidden and visible ratings.
If you win a lot, your rating climbs until opponents are as good as you are, so you should settle near a 50% win rate. That is the system working as designed, not the game punishing you. A losing streak is also normal: with a 50% chance per game, streaks of four or five losses happen regularly by chance alone.
What actually helps is the same everywhere: play enough games for the number to find your level, review the matches you lost instead of only counting them, and take a break when you are frustrated, because tired play lowers your real skill below your rating.
Can I trick the system into easier games? Not for long. Deliberately losing lowers your rating, but as soon as you win again the system pushes you back up. It also hurts the players you are matched with.
Is it unfair when a teammate is much worse? Over many games, teammates average out. In any single match, one weak link or one lucky streak can swing the result.
Does each game work exactly like this? No. Companies rarely publish their exact formulas, so treat this as the basic idea that most systems build on.