Sirer is the creator of the first cryptocurrency to use a proof-of-work concept, The Karma System. A major figure in both Bitcoin and Blockchain academic research, he has contributed his technical expertise to multiple projects, including Ethereum smart contracts. He is known for his contributions to peer-to-peer systems, operating systems, and computer networking.
You should only invest in and hold coins which you believe will be used, extensively, in the long run. If you bought coins on a whim, without an investment thesis, based on hype, well, they are pure speculation.