The success of Flappy Bird seems to have confounded a lot of people, who can't seem to understand why it's such a big deal. As a game designer, I see some very sound reasons (based on core design principles) why it's so darn popular and addictive, despite being so brutally difficult. Here's what I think :
It feels winnable
The objective of Flappy Bird is very simple - "Score 1 more point than I did last time". That is all. No quests, no story, no faraway goals that seem unreachable or intimidating.
That doesn't sound so hard, does it? Surely you can do it?
Especially since you were this fucking close last time. Right? You only missed by a whisker. So you try again.
Play time is super short.
Each play lasts, for most people, about five seconds or less. Even the best players can't be playing for more than a minute. So where's the harm in trying just once more to score just one more point? So you try again.
Every small victory makes you feel Like A Boss.
Because it's so darn hard, scoring a single point gives you a feeling of epic victory and accomplishment. And the next epic win feeling is only five seconds and one point away. So you try again.
It feels fair
This is important - the basic physics and controls in the game feel solid and fair. So every time your bird falls to the ground, you blame yourself and your lack of skill. Not luck or randomness. So you still believe that you can beat it the next time. So you try again.
So by following four very basic design principles and implementing them well, the designer has created a game that is addictive. A game that people can't stop playing. A game that people talk about and get others to play. I don't think it's an accident - it is at its core a very well made game.
It isn't even the first of its kind - many recent games have achieved success by following the exact same principles. Super Hexagon, for instance. It's just that Flappy Bird takes these principles and distills them to their essence, cutting out even the most basic of embellishments, such as pretty graphics, music or a story. Which is why it works for such a wide audience. And which is why it will fade away quickly - because it lacks lasting value to anyone other than the most competitive of players.
The lesson here for anyone making games is this - the oldest video game design technique (one fun core mechanic tied to a high score ) still works very well.