There is the idea of having an emergency fund, which given its nature, should be stored in an instant access savings accounts.

This is money for when you lose your job for instance

Your appetite for risks and circumstances determine how big it should be (a good rule of thumb is six months worth of salary) but there are countless stories of people trying to be clever with their emergency funds and storing them in ETFs or riskier investments only to find that when the need comes, their fund is not enough and get in financial distress.