Classic examples of speculative bubbles include the tulip mania that swept Holland in the seventeenth century, and the South Seas bubble which caused the first big stock market crash in England in 1720. The more recent three examples I have cited were mild by comparison with these earlier ones!
Although bubbles may persist for quite some time, experience shows that asset prices eventually return to a level that is more consistent with “the fundamentals”. Bubbles do reveal themselves in the end - people are not fooled forever. Eventually mistakes in pricing become widely recognised, and markets correct. This makes bubbles inherently temporary, involving first expansion and then contraction.