Agreed 100%. Golden rule. However, currently I'm ignoring this and mining LTC at a ~10% loss because:
a) I have no money to buy coins because life happens AND
b) My electricity supplier put me on pre authorized monthly payments of 'x' no matter what the monthly bill is. The excess or deficit billed annualy will be adjusted in a bulk payment/refund sometime in the middle of next year. Figured a year was enough for crypto to recover and I am kind of getting interest free loan in electricity to "buy"/"mine" crypto.

Gamble? Informed risk? Dunno.

On the bright side, a few Z9 mini's are actually offsetting the current loss so the mining operation on the whole is in the green.