It is really important to know the process of painting a surface and to know which products to use. Many home-owners are not aware of the reactions a product can have if you don't use it on the proper surface that you'll be painting on. Many products are different from others, so it is extremely  important to know what you'll be using.

 For example: If you don't use the proper paint or primer for an exterior stucco wall you could have major consequences in the future, your walls can crack or peel off within months. Having to repaint it plus do the harder work which is sand and peel off  falling paint due to using improper paint/primer. Making it more expensive to repair and time consuming.