Not true. As another posted mentioned, in trademarks, if you don't protect the right, it might become genericized, but not patents. Unlike a trademark, which does not have a fixed time period, a patent is 20 years. You do not lose your rights just because you do not police your patent in those 20 years. Does it make it harder to license it to an exclusive licensee if you are not policing infringements? Absolutely. But you do not lose your rights if you chose to my police.
Disclaimer - I am an IP attorney. This is not legal advice, only legal information.