Keeping it idle isn't so bad your already gambling by keeping it so why "invest" it somewhere else, that's just more gambling lol
I think the investment is not a sort of gambling. does not require the skills of an investment. but the investment is not gambling. if you do not like the investment. there are many other ways that better than keeping it idle
keeping bitcoin is not a gamble, it is an investment and just like any other investments it has risks so invest what you can afford to lose. besides the chance of going up is higher than going down.
also i might add, it is a good idea to invest bitcoin too. because you can have the opportunity to gain more bitcoin as profit if you invest. but finding a good investment is hard and you have to search for it. the best one IMO is investing in Altcoins.