The standard business cycle used to be 54 months. I learned that in the 70s and it was a consistent time frame dating back a hundred years, including the Depression. (I know the Depression lasted a lot longer, but the cycle still held up to some extent throughout the thirties.)
The Fed has gotten a lot better at moderating the swings, and lengthening growth periods, so it isn’t as awful as it used to be.
The business cycle is much different from bubble periods like the dot com boom/bust, and the real estate bubble. The real estate bubble was caused by fraudulent behavior; that can be hard to avoid.
The current bubble really only applies to crypto currencies and cannabis, but there are three major things to be concerned about:
1. A difficult Brexit disrupting European markets would spread to the US.
2. The GOP tax cuts coupled with increased defense spending is adding huge debt with little benefit.
3. Increased barriers to trade are already disrupting agriculture and manufacturing.
All three of those issues are easily avoidable, but not at all popular to address by the Administration.