Tooth pain why

 Tooth pain occurs by your default. How .
I will exlaexp.

When u don't brush properly twice a day,the food remain intact with your teeth.

The bacteria get chance to enjoy their party and increase their numbers and release acid that destroy your tooth.
When bacteria reach upto pulp chamber  and move further upto apex of root and start growing in number .
The pain starts.

Then doc suggest you to go for RCT that is root canal treatment.