I did not make the mistake of buying a big house on the promise that in the future I'd be able to afford it. A friend of mine bought his house and his neighbor's house to combine into a larger lot, but since the stock was going up he got jumbo loans and was selling stock periodically to make the payments. When things went south he ended up selling the neighbors house at a loss refinancing his own house at a lower rate to stay in it affordably. But I did make the mistake of not paying off my house when I could have using "bubble" stock (like that Sun stock). 2001 to probably 2006 were very wintry years.
I analyzed my behavior during the last dot com bubble and my biggest driver was tax avoidance. How stupid is that? I would say "sure this stock is 'worth' $500K but if I sell it I'm going to have to pay a huge amount of tax on it and that will net out to a smaller number." I was looking at "losing" 25% of the value of the investment by turning it into cash. Ridiculous right? Well now I think it is ridiculous.
Every 3 months I take a long look at my assets and debts and future plans and re-balance as necessary to avoid a single thing from killing me financially.