Not all smart contracts are smart like we think they are. Smart contracts like the ERC-20 token standard held digital assets worth over 4 Billion US (in early 2018) these assets are not always as secure as we wish or as we think they are, as an abundance of hacks and bugs have proven. This puts a significant burden on the crypto community. Especially new investors that buy on the hype before doing much research. Unfortunately, when there is a hack or a huge bug it is more than likely reported in the news and we rarely hear the positive events.

https://news.callisto.network/why-do-we-need-smart-contract-auditing/