I keep reading in this thread that you need >50% of a network’s hashrate to perform a 51% attack. This is not true. Having >50% of the network’s hashrate only increases your odds of being successful. A bit of good luck could reduce the needed hashrate greatly.
51% is used because this type of attack is not just about finding and replacing a single block, the attacker has to be able to make their own chain longer than the rest and it is increasingly difficult to do the less hashrate the attacker has. In other words they may get lucky and find one block fast but the second block isn't going to be as easy and the third could be near impossible to find faster.