What are the reasons of overheating cooling fan?

To All Techyv Members:
What are the reasons of overheating of the notebook cooling fan despite the manufacturer’s of different brands continuously designing a better and greater speed? Why these notebooks are still susceptible to overheating despite cooling fan is being installed? Why is it so despite the cooling system is installed? Is there any new product that ventilation will not be clogged anymore or will no longer be impaired despite usage in normal conditions? I am so much afraid that this will lead into a fire in the house and will create more problem. This will be another problem as a consequence of using the notebook.
