Tooth decay normally doesn't hurt.
Its kind of like your dishwasher blowing a gasket, or something similar.
You think everything is fine and then the next moment there is
water all over your kitchen floor.
Well the dishwasher didn't go from brand new to breaking down over night.
It took a while and if someone trained in dishwasher repair had been
called out to occasionally check things out then the problem may have
been caught prior to the disaster.
The problem is that to you, the untrained eye, nothing is
wrong until things are very wrong.
The picture above is a progression of decay.
Typically it is not until step 4 that you would feel any major discomfort.
Problem is that steps 1-3 can be fixed with fillings and step 4 is a root canal.
You don't wait till your engine starts smoking to change your oil.
Please don't wait till you are in pain to have your teeth checked.
Lots of time, and discomfort can be avoided this way.