Never catch a falling knife.
When you’ve invested time, money, and energy into something, the default human instinct is to double down and keep on going even though the original premise might already be gone. If you do this, you just try to justify the past. That is the sunk cost fallacy. It might not be better to continue like before. This applies to pursuits, relationships, hobbies.
You could find yourself in a pit anywhere.
A good gardener doesn't hesitate to cut dead branches before the rot spreads. Nobody likes to admit they were wrong, but repeating is the mistake in the first place.
Recognizing sunk costs early on is great leverage. If you hesitate and don’t simply know, the answer is always no.
As Seneca famously noted: if you are endlessly reminiscing about the past, you are bound to be unhappy. Act accordingly.