One of my favorite sentiment checks is how much the e t fs buy. The last two days saw $1.6B in buys. Add that to the amount treasuries bought last week and you get the rally we've enjoyed.
The more you fire a neuron, the more likely they are to fire again. Also the more likely to fire the next neuron down the path is.
The first time you fire them you are cutting a path through brush in the jungle, the more you do it the easier it is.
This is good and bad, helps habits stick but also makes bad habits stick.