Mining Difficulty

Mining difficulty is a relative measure of the competitiveness for discovering blocks on the BTC network. It rises or falls based on the amount of computing power consumed by the network. 

Since for each mined block the amount of bitcoin offered to the network is the same, the mining difficulty is a measure to regulate the miners' gains. 

It varies according to the number of miners online (thus the mining power available on the network).

In a simplified way :

- The more there are miners on the network, the more the difficulty of the miners will increase and therefore the more the gains of crypto-money per miner will decrease. 

- On the contrary, the more there are miners on the network, the more the difficulty of the miners will decrease, so the more the gains in crypto-currencies per miner will increase. 

This is a very important variable to take into account and to study before you invest in mining. 

Warning: It is possible that your miner is currently very profitable, but that over the next few months the difficulty increases strongly and this one is much less profitable. 

More resources on the subject: 

https://blog.sesterce.com/

https://www.blockchain.com/charts/difficulty

https://btc.com/stats/diff