One of the singular most easy to overcome problems in painting is that of adhesion.
Paint will not stick to a surface that is not properly prepared and yet it is the most under performed step in painting anything.
Two of the most important steps that if not completed properly or left totally undone causes more paint failures than almost all other steps combined.
Wash the surface, abrade the surface …. …. sugar soap and sand paper …. …. wash it down, lightly abrade the surface and you are on the road to a great paint finish.
Failing through the lack of sanding!!