something to do with difficultly. (Don't know much about it)
As stated above. Stop. Get yourself a cheap GPU or maybe a single ASICminer USB. Play with them. Learn about mining. Spend lots of time on these forums, reddit and the Bitcoin wiki. If you continue straight down this road without proper knowledge of how Bitcoin mining works, the technicalities of it and the history, you will be unable to make proper decisions with regards to investments.
If you decide to go ahead, I have the following advises:
-> Have a thorough, not just surface understand of difficulty re-targetting. When you can properly model your own estimates, you will realize that these "online calculators" are absolutely useless until the difficulty settles down to be consistent again. ie, after a significant number of ASIC companies are consistently shipping in bulk. Make your own models and trust yourself and your research, not others.
-> Further on the above point, understand even the small details of mining, such as understanding the average time between blocks is often less than 10 minutes when network difficulty is increasing rapidly and what that means. There are many small details you might want to make a mental note of with your estimates but not actually write down.
-> Have practiced mining small-time with GPUs or a block erupter and be able to deal with any issues that arise. Downtime. Miner failure. Miner issues. Software issues. Heat. Expansion. Maintenance. Etc. This is computer knowledge and technical knowledge. I don't recommend someone mine if all they can do is put together a plug-and-play solution.
-> Security: Keep your coins safe.
-> Because of "something to do with difficulty" combined with the fact that most ASIC orders that will make a return if received now are either backlogged or still pre-orders and non-existent, you will have to pay attention to the ASIC market and make mostly pre-purchases when A. They make sense based on the manufacturer's estimates and B. They fall within your risk limits financially and by the amount you trust the company.
-> Adding on to the above, diversify for this exact reason. To mitigate risk. The problem with that is diversifying will require significantly more capital due to the high cost of even the lower-end units from many companies.
-> Track everything. Track your financials. Track your balances. Track the market. Track the ASIC companies' progresses. Understand what you are potentially getting into.
As a sort of summary of the above, let me make it clear that mining is no longer a small-time game as it used to be. Mining for returns now requires capital and proper planning. The days of the hobby miner making a return after a few days on the forums and a digital trip to newegg, are gone. Serious miners are who are emerging now. If you intend to make money, you can no longer buy whatever and start mining like you could last year.
Now, that said, if you want to do this as a hobby, buy something you can get now or soon, such as ASICminer equipment and do not expect a return. My modelling indicates a 12 month return of 67% of your original investment. I personally don't like modelling more than 6 months though due to the unpredictability of everything Bitcoin. Besides, due to the difficulty, most of the return of that 67% will be within the first 4-6 months if you get the unit right now.
