What do I need to know about mining difficulty before starting a bitcoin mining startup? I am working towards starting a bitcoin mining startup in China. I can do the profitability from various calculators available online but I need to know about the difficulty level. The difficulty level has increased in the past, causing dedicated devices like antminer s1 to become obsolete. What should I know about difficulty?
If you want to extrapolate what the difficulty will be in the future, here is a chart you can look at:

http://bitcoindifficulty.com/

The big thing about difficulty is that it's hard to predict. In general, it's almost always increasing due to better hardware, but it's hard to predict how much it'll increase because bitcoin hardware increases with innovation, something that's intrinsically hard to predict.

Generally, there's a lot of guesswork involved and forecasting to do as a businessman.