how come this happen?

how come somebody can do the right thing/ belaying action, then revert to do wrong (belaying action) again.

absentmindedness? habit hard to break? even though one may/ may not know the reason behind the reason the action is right/ wrong.

how about other aspects of life?

Maybe by not learning the correct method first and falling into an old habit - but the most common is by not paying attention.

Almost everytime l have made a mistake or l have seen someone else make a mistake it was not because they did not know or had not been taught - it was not paying attention. If you are going to do more than one thing at a time, be especially attentive to things that would otherwise be routine.

Good Luck

Sometimes it is confusion between multiple techniques. They learned one way, retaught a 2nd way. they may not be as comfy w/ the new method so they sometimes revert back out of habit & comfort level. Sometimes this is due to a panic/stressful situation. Belaying for instance can be stressful sometimes if ur climber is moving too fast for u to keep up for beginners, so they do incorrect things to try to catch up & in the process r putting their climber in danger. l teach people ''whoever wants to go slower wins meaning ''if the climber is going to fast, the belayer tell climber to slow down for the sake of their safety.''

There are several reasons:

1. They are not doing it wrong, just a different way (maybe different from the way you've learned).
2. Like you said, absentmindedness (or tiredness).they maybe learned an incorrect way, later learned the correct way and just forget revert back to old habits.

Maybe instead of posting your questions to , why do not you (gently) correct them and help them become a better climber? It is about safety you know.