In case you didn't already know ...
Did you know, bitcoin mining is basically the same as dice rolling?
There are many articles for non-technicians about bitcoin mining, where the mining process is often explained as "solving complex equations". And these equations get more complex, when more miners compete, so the difficulty raises.
First of all, to be pedantic, these "equations" are inequalities, and these inequalities have the basic form of
f(x) > Difficulty
whereby f is a so called hash function and Difficulty is an integer value, automatically adjusted by the average time needed to solve a series of inequalities in the past. To mine some bitcoins you have to find an x which is greater than the current difficulty.
From a non-technician view we can describe bitcoin mining as follows.
You roll a die until you get a number greater than the current difficulty, whereby the difficulty is in a range from one to six.
Imagine you are the only miner, and the difficulty is three, then you will roll in average every three dice rolls a number greater than three, so you will get in average every three dice rolls a certain amount of bitcoins.
Imagine further, you need for one dice roll a time of one minute (In reality you might be faster), so you will "mine" every tree minutes a certain amount of bitcoins.
Now another miner enters the game and rolls his die too. But you and the other miner don't roll the dice in turn one after the other, you both roll your dice simultaneously. The other miner can roll the dice as fast as you, one throw in one minute. So you still get in average every tree minutes a certain amount of bitcoins, and the other miner will also get in average every three minutes bitcoins, which means you both together now get in average every 1.5 minutes bitcoins.
And that's the point where the difficulty raises, because in the bitcoin system by design the difficulty is always adjusted to such a level, that a constant amount of bitcoins will released in a certain time range.
Let's say our time range where three minutes, so the difficulty should raise to five now in our example, so you and the other will get in average every six minutes a number greater than five, and both together in average every three minutes.
That's the basic principle of bitcoin mining, dice rolling, but for bitcoin mining a die is used with 2256 faces, so the difficulty can be adjusted from zero to 2256 which is a very huge number.
Now it is easy to explain, how a faster computer or ASIC or whatever can mine more bitcoins. A faster computer means, you can roll the die not once a minute, but you can roll it perhaps every then seconds, and if you are using two computers you are using two dice using both hands to roll them. As more hands you have, as more dice you can roll.