What most mining newbies oversee is how the more or less steady grow of global hashrate and thus difficulty continuously lets your own, usually constant, hashrate earn less and less, because your share to the global hashrate gets smaller and smaller. This is one of the main profitability killers.

If your investment in an ASIC needs about one or two years to break even, and the usually ridiculous prices of state-of-the-art ASICs demand quite long break-even periods, you should have a look how mining difficulty changes over such period intervalls.

Compared to a year ago to now difficulty rose about +46.3% (a year ago set to 100%); compared to two years ago to now it rose about +145.5% (see difficulty chart).