How to express that you wish something had been different. Closely related to conditionals Type 3 and wish + past perfect.
Each expression of regret says the OPPOSITE of what actually happened:
Reality: I didn't study. (negative)
Regret: I wish I had studied. (positive in the regret)
Reality: I went out yesterday. (positive)
Regret: I wish I hadn't gone out yesterday. (negative in the regret)
= a missed obligation in the past. "I should have revised more" = I didn't, and I regret it.
If reality is negative, regret is positive. If reality is positive, regret is negative.
I regret doing X (regret about the past). ยท I regret to inform you (formal, present moment).
This function works in tandem with grammar Unit 9 (conditionals + wish). Master both at once: they share the same mechanics.