I would not underestimate the risk.
There are a lot of things that can go wrong.
The price can decrease because of another crypto currency, your wallet can be compromised, your keys can get lost.
An Investment in bitcoins is something you have to keep an eye on.
Just buying the coins and sitting back, I don't think that is a whise recommendation.
I think there are two types of risk, the risk inherent of bitcoin as an investment and the risk of managing your bitcoins, about the latter I do not think it should be considered since any currency suffers from the same and about the former, bitcoin can be unstable in its price but this risk can be cut down a lot by just holding long term.