Should we still mine nowadays with CPU/GPU? For the little bit I understood so far about the mining process, it seems to me that "finding" a block is very very very difficult for a CPU/GPU.

However, since it is done by brute force, it seems to me that there is a very small chance (has anyone calculated how much?) of a single cpu miner to find a block very fast in a few first tries, hence hitting the jackpot of 25 BTC.

Is this theory correct?
it is now impossible for normal CPU/GPU to mine bitcoin, you need to get some ASICS or Gpus (e.g Rx480) and mine in a pool. of course you should buy devices with high Hashr power to increase your chances to get rewarded. Here is a simulator to check the potential profit you could make by determining your hash power : https://www.cryptocompare.com/mining/calculator/btc

some details about the mining pool and the network hashrate :

https://btc.com/