Well exactly. I don't know what you're imagining, but I just said "some retirement income", I didn't say I'd be able to retire on them alone. I also didn't say "major" investment; you made that up.

Sure, the price of a bitcoin varies a lot in the short term. So don't worry about the short term price, just look at the long term price trend.

There's no way to make the short term price more stable while Bitcoin is in its early phase. As you've pointed out, the short-term price fluctuations don't mean very much, so why worry about them?