I guess I have to explain. The reason it’s a definition of a bubble is due to compounding. If the economy is growing at 1 to 3% while equities are going up 7 to 10% a year they diverge slowly at first but the divergence is exponential. What ends up happening it takes far more debt to sustain this bubble. Interest have to keep doing down so the payments stay relatively the same but at some point rates can’t go lower or a shock causing the ability to pay goes away. Then the bubble pops causing a liquidity problem(2008, March 2020) causing a massive sale off of the most liquid assets. So far the governments of the world have been transferring the liabilities of the most toxic liabilities from banks, pension funds, etc to the Central banks. It is an asset swap and doesn’t inflate the money supply directly but what it does do is tell banks lend all you want if you blow yourself up we will bail you out. This further inflates the debt bubble since banks now believe the fed has backstopped their loans there by limiting downside risks. This money being created has to go some where so it goes into asset purchases. Then you have margin and loans based on the assets further inflating then bubble. This creates a feedback loop since the increase in the asset prices increases the amount of money available to borrow which is often used to buy other assets further increasing the price.
Yup, it's literally just "being bearish". If you want to see people "being bearish" or "being bullish" just flip on the CNBC or something and listen.
You either claim that the interest rate (or various risk premia) are too low, or that the estimates of future profits (for whatever reason, higher COGS, higher cost of labor, higher taxes, under-measured depreciation and higher capex, natural calamities, lower GDP and thus lower revenues, or really any other reason) are too high.