Museums preserve historical pieces just like individual collectors, but museums hire staffs who assemble collections with great care and study. Great collections are built on knowledge, study, perseverance, a good deal of luck, and money. If you read about anyone or organization who built a great collection, be it art, or otherwise, it was always done with someone in the chain acting as the "knowledge" base. Someone has to know what to buy and why. Whether it is a dealer with connections or the collector him or herself, the knowledge aspect has to be there.
Knowledge can be the result of long-term experience or dedication to the accumulation of a specific area. There are collectors who build collections by themselves, who study and assimilate information. But there are precious few collections which are not built on a strong base of information. This is why collecting tends to follow the publication of knowledge in one form or other. In the past, it was books, now it may be the Internet. If you decide to collect in the high-end of any collectible, who are you going to look to for verification and advice?
There is another type of collector who just walks into a show, approaches a collector who has a display they want to buy and says:..."how much?" The owner says: "it's not for sale." And the 'buyer-collector' says: "No, you don't understand. How much do you want? Price is no object." This kind of collecting requires no knowledge, just money. It's not collecting, it's shopping. It also tends to be self-limiting, because there are not many collectors who will sell under those conditions and the buyer soon burns out. There are individuals in the current market tossing around six digit figures in the desire to buy whole collections or "invest" in the antique market. They usually pay too much, get less than they paid for, and go away after a short burst or when they figure out they are the laughing stock of the hobby.
Part of the fun of any collecting is figuring out what is rare and what is not. For some people, possession of something other people want is a driving force. There are collectors who just collect what appeals to them personally and that is fine, but when the time comes to sell their collection, one can only hope their tastes are shared by others who want to own and possess similar items. Otherwise, you don't have an auction, you have a garage sale.