Three possibilities to consider...
1. You're pressing the water saving button (piss flush)
2. You're not holding it down for long enough for it to catch - it can take even a second in some poorly maintained toilets for it to flush properly.
3. Your diet could do with some _serious_ improvement...
That being said, I'd rather having to double flush than deal with clogs as when visiting the US.
The European-style flush relies on buoyant waste getting carried away by the mass of water - which isn't the most reliable strategy.
Three possibilities to consider...
1. You're pressing the water saving button (piss flush)
2. You're not holding it down for long enough for it to catch - it can take even a second in some poorly maintained toilets for it to flush properly.
3. Your diet could do with some _serious_ improvement...
That being said, I'd rather having to double flush than deal with clogs as when visiting the US.