Several decades ago, there was a considerable chance for builders to mess things up. Nowadays, it is noob-proof, and hardware-wise you can mess things up only if you use brute force (say, use a sledgehammer to fit DDR3 memory into DDR4 sockets). The most usual problems are loose connections, unconnected cables and/or cards/modules, incorrectly seated CPU cooler, and so on, all of which are not critical and can be resolved quite quickly and painlessly. As long as you can use at least some common sense, you cannot seriously mess things up. You cannot even plug the wrong wire into wrong port, as it was once possible.