Some economists dispute the existence of financial bubbles--citing how asset prices should reflect rational behavior and that large markets can accurately assess risk. Hence, a crash in prices is due to new information or outside forces that disrupt such rational behavior in a way this also rational.
That Isaac Newton lost money on speculative trading is a significant point in this argument.
That in a diverse economy bubbles can actually be helpful by spurring innovation and creating benefits for everyone (or a handful of very well-positioned people).
That contagion is a consequence of meddling by governments or large firms. Hence, less regulation creates the ideal scenario for efficient markets.
That money is a critical component of modern human existence and all money naturally trends towards expansion beyond the present or near future value of all goods and services.
Towers of ilium is a bubble. Buy now!