Keep in mind, in March of 1929 the stock market had a mini-crash, similar to what we saw after the mess of the markets a year ago. Not a full crash; but it was one hell of a drop. Things rebounded and as the market seemed to heal, people forgot or disregarded what had happened and over the summer things were nice and in September of that year, things hit a new high. Forwarding to October of 1929 and Kaboom! The market took a dive which nobody had foreseen. In point of fact, after the September rally, even more had figured that the good times were back, which made the October events-Black Thursday, where on October 24, prices fell sharply and people were selling like mad. Bankers got together, threw their money in, the selloff ceased and calm returned in time for the weekend. Then came Tuesday, October 29, and we know what happened then. (if not read up on it at your local library or do an Internet search and learn more). Part of what triggered the big crash was the nervousness which took over after the events of the 29th. When things looked better, people decided to get out. Sell their shares, rake in whatever profits they could. The result was Kaboom!
In November of '29 there was another dip, and the markets did poorly for a few years after.
A similar disaster could happen here if people who are invested in the market decide to get out now. That amount of selloff could conceivably cripple the market more than what we saw in that last drop.
Mind you, I am hoping the market will maintain its slow steady growth; but, I am not yet fully convinced we are thriving. The job market is still a wreck. costs are still high, people who have jobs have had salaries frozen, while their expenses have risen. A healthy stock market is not proof that all is well. Hopefully things will get better all around.