When decision makers choose to continue an existing course of action because it is the less painful option at the time, this is known?

It is known as the Prospect Theory Effect.

Prospect Theory is the tendency to feel stronger negative emotions than positive emotions when losing something of value. It is an assumption that losses and gains have different values even if they are really both equal. For an instance, there are two options presented - one shows potential gains and the other shows possible losses. The former option will be chosen because the probability of gain is perceived greater.