Sweet & sticky food mainly
Acid production and bacterial attack
Gradual destruction of tooth material
Cavity(continuously progressive)
1) If decay is superficial (In Enamel & Dentin):
Your decayed part of tooth is cleares out by removing decay & artificial filling material is placed to secure the tooth
2) If decay is deep (Extending in to pulp) 
Root canal Treatment Read More Need To Be Done
3) If infection spread beyond tooth in the bone (Periapical Infection)
Tooth may not be able to survive for longer time & chances of spreading infection to adjacent tooth & bone so Removal of that tooth is advisable as a Permanent Solution.
