However, you should be cautious because people aren't very good at being random, and there are automated programs called bots that have managed to figure out many keys that people have come up with using their brains. This is because humans aren't good at being truly random.
Another reason that the members did not mention is why you want to choose the seed words yourself? Mostly the answer will be to remember it, but you will fail to remember 12 words. You can memorize up to 6 words. Some may reach 10 words, but 12 words are a lot, and failure in one word or its arrangement will be very costly.
This is if we ignore the possibility of memory loss due to accidents or trauma.
The compromise solution is to generate seed words and try to link them to something you remember, such as trying to make them into the lyrics of a song or poem, or encoding them and hiding them in several places instead of choosing the seeds yourself.