What are achievements and trophies actually for?
They are a secondary goal system layered over a game, and they serve players and platforms in quite different ways — which is why they range from genuinely enriching to plainly manipulative.
What they do for players:
Extend replay value by rewarding things you would not otherwise try — finishing without a particular weapon, finding every collectible, completing under a time limit.
Surface content people miss. A surprising amount of design work goes unseen, and an achievement pointing at it is a curatorial act.
Provide structure after the story ends, which is otherwise a vacuum.
Act as a record of what you have played and done, and a shareable one.
Suggest a self-imposed challenge with a defined endpoint.
What they do for platforms:
Increase engagement time, which is measurable and valued.
Create ecosystem lock-in. An accumulated gamerscore or trophy level exists only on that platform and does not transfer, which is a genuine switching cost — and one of the least discussed reasons people stay with a console family.
Enable social comparison through leaderboards and profiles.
Where the design goes wrong:
Grind achievements demanding enormous repetition with no skill component — ten thousand kills — which measure patience rather than accomplishment.
Multiplayer achievements in games whose servers will close, making 100% permanently unobtainable and rendering the list a trap.
Missable achievements requiring a full replay because of a choice made hours earlier.
Luck-based ones, dependent on random drops.
Achievements that spoil the story by appearing in the list before you reach them — a genuine and avoidable design failure.
The psychology. Achievement systems work on completion bias — the discomfort of a partially filled list — and on variable reinforcement. This is deliberate, and it is the same mechanism used more aggressively elsewhere in games.
Whether they improve games is genuinely contested: some research suggests external rewards can undermine intrinsic motivation, so playing for the trophy replaces playing for enjoyment. Well-designed lists point at interesting play; badly designed ones replace it.