Locks are strong against an unskilled opponent. But if you give your friend a locked box to use, you have to provide them with a way to get the key at some point so they can open it.

If you sell these boxes to millions of people, someone you sell it to is going to have some skill and know how to copy or modify a key, and then start giving keys out to other people do that they can also open the boxes, even unauthorized ones.

So a video game is just a collection of files which can be copied at will to any computer. An important subset of this files contain executable code, a program. Now in principle any computer could run the same code, but the publishers of video games want to restrict the users of their product to those who paid for it.

One way to do this using physical media, e.g. DVDs, is done by removing important pieces of the code (or encrypting it) which is stored in a normal fashion on the DVD. Then at startup of the game, in order to continue it requires these pieces (or a key for decryption) and reads them from parts of the DVD which is hard to copy exactly, so people can not just create and distribute copies of the DVD. This works because end-user DVD burning equipment has much higher read-fidelity than write-fidelity. A skilled cracker could analyze this process at the program's startup and just patch the missing pieces directly into the program and upload it.

A much better and modern approach is DRM like Denuvo. Obviously the companies who make DRM are quite secretive about its working so we have to rely on the crackers who try to circumvent the protection. It usually works by online-activating the program of the game and fingerprinting it to the end-users environment and hardware. So every user then has a slightly different program installed which at startup or even while playing tries to make sure it is run at the very same computer on which it was activated. A cracker must try to analyze the program, which had a lot of senseless data added (obfuscation) in order to prevent being analyzed. They then have to find all functionality in the program which prevents execution on the wrong user hardware and remove that parts of the program. Finally they can upload a program which runs on any user's hardware without online-activation.

PC owners technically have full admin rights to their operating systems, therefore with the correct knowledge and tools, they are able to inspect and modify any aspects of any programs running on it, including any game DRM checks.

Therefore all modern PC anti-piracy schemes are built on the principle of obfuscation, just scramble the piece of code and make it a huge headache for a human to descramble and reverse engineer to skip all the checks.

Therefore it is only a matter of time before all the checks are found. PC game publishers now only uses this time difference to cover themselves to sell most of the expected sales, and update the game once one major version has been cracked to protect their online gaming services as much as possible from cheating.

Console disc-based copy protection however still relies on hardware. Discs are produced to contain errors that are genuinely impossible to replicate as long as you don't have the original stamps, and the disc drives contain special firmware to look for those errors. Consoles check these areas to determine if a disc is genuine or a burned/pirated pressed copy.

Console digital copy protection works on the assumption that console owners DO NOT have full admin rights to the OS, and therefore the hardware encrypts EVERYTHING to prevent inspection and modification of the code as much as possible, guarding the code even from users.