With Bitcoin today, instead of needing 4 leading zeroes you need something like 17 leading zeroes (in hex, or ~1 in 2^68 chance of finding a block). Every 2016

With Bitcoin today, instead of needing 4 leading zeroes you need something like 17 leading zeroes (in hex, or ~1 in 2^68 chance of finding a block). Every 2016 blocks, the difficulty adjusts. This is supposed to take 20,160 minutes, but if the timestamps indicate that it took less than that, the difficulty will increase, requiring more leading zeroes. If it takes more time than 20,160 minutes, the difficulty will decrease, essentially requiring less leading zeroes. Also worth pointing out that the hash can be evaluated as an integer. Instead of requiring an exact number of leading zeroes, you require the hash to have an integer representation than is lower than a certain value. There's actually a lot of work that has gone into Bitcoin to make sure that having higher hashrate and higher influence does not make it more likely so that you can find a block. Ideally, if you have 0.01% of the hashrate, you have a 0.01% chance of finding each block, and if you have 33% hashrate, you have a 33% chance of finding each block. In reality, Bitcoin is not quite this perfect, but it's pretty close. The 33% hashrate miner may have a 34% or 35% of actually finding each block.