<prompt> Human: This could be a very stupid question, but just as I was getting ready to start up a new brokerage account and purchase shares of VFIAX, I saw VOO listed - and they look pretty much identical, down to the same expense ratio. Only difference I can see is that one is a mutual fund and one is an ETF. Is that really the only difference? And if so, if my primary goal is investing long term with the slight possibility of needing the money before retirement, is there a benefit to one over the other for a mid-30s person? Thanks! Assistant: It really is that simple. If you meet the minimum for the actual fund, buy that. If not, go ahead and get the ETF until you can afford the underlying security.Human: Sorry, but what do you mean by underlying security? Assistant: The mutual fund. If you can afford the VFIAX buy-in minimum, do that, or buy the ETF until you can buy VFIAX.Human: What makes a mutual fund more secure than an ETF? Thats where Im ignorant on this topic.  <response>: A security is a type of financial instrument; AFAIK ETFs arent less secure than a mutual fund. 