Humans have a mutation to the myostatin gene which makes our muscles much weaker than they could be. It’s thought that this evolved as a way of conserving energy for our ridiculously overpowered brain (which uses up about ⅓rd of all the body’s calories as it is). In fact, a small handful of people are born with the myostatin gene mutation undone, which leads to a condition known as hypermuscularity where young children end up with a bodybuilder’s physique of rippling muscles and a toned six-pack. Animals like gorillas do not have this mutation, which is why they are immensely stronger than humans.
Ourang-outans can rip a human limb from limb with relatively little effort; the massive silverback gorillas are much, much stronger. Even the strongest human weightlifter is no match for a gorilla, muscle against muscle. Of course, we gave up those muscles for brains and it was a very good bargain, since even the smallest, weakest human with a gun can take down a gorilla with ease.
(Quick edit: I just confirmed with a Google search that gorillas can lift more than ten times their own weight with ease – that is, the weight of more than thirty humans – and they may be able to lift even more; no one is quite sure, since there’s no way of knowing whether a gorilla is exerting themselves to the maximum when they lift something heavy.)