Everyone's different. Perhaps your grandmother relied on a fair...

Everyone's different. Perhaps your grandmother relied on a fair amount of luck but I see luck as only a small part of investing and I never rely on good luck for my gains. However I try and diversify to some extent to reduce the impact of any potential bad luck. That is; bad news that was difficult to foresee.
An example is buying MWR over the last month or two when everyone had gotten bored of waiting for news but the sp had stopped falling. I bought just over 8,000 shares at an average $3.25. A few others got a better price. We knew there was a high chance of the company delivering what they promised. I'll be surprised if this isn't trading above $4 soon enough. Was that relying on luck or applying some funds to a high probability trade? Before you go accusing me of bragging again, I'm only stating it as an example of my point of view.
So while luck will play a small part, it should only be a small part unless you're just gambling rather than investing.
Your grandmother is probably right not to invest in this stock at this early stage. Stable income stocks would be more suitable for a retiree. Having said that, when I get to my retirement age I'll probably still dabble in the early stage companies like this as well because that is where I get the most satisfaction.