> And if you're making a big financial decision like whether you can afford a bigger house, I sure hope you're treating them the same.
On the contrary, I would suggest most people ignore their equity such as stock when considering whether or not they can afford a mortgage for the very reason of this thread title.
> And at the end of the day even the nominal value of cash isn't what matters -- it's the real value.
I prefer to use the term “purchasing power” rather than “real value”, but I agree with this.
>Inflation and even currency fluctuation change the real value of what your cash can purchase daily, so the value of your cash is changing too.
Correct, which is why buy equity such as stock or broad market ETF. I think the purchasing power of the equity will be higher than cash sufficiently far into the future.
But I do not see the point of worrying about decreases in equity prices in the near future long before I plan on selling. I guess there is no right or wrong, but I feel like worrying about short term changes in price is how people actually lose money by selling low and bugging high, rather than just buying and holding.