What color is the paint, or more importantly, is a deep pigment base with a lot of pigment added?
Some colors, particularly deep reds and greens, start with a deep tint base and add tint to it. It is difficult for a DIYer to get all this pigment evenly distributed. You need a practiced hand and you need to work fast, keeping a wet edge. Rolling techniques are different for deeply pigmented paints.
Quality tools are also critical. Cheap roller sleeves and cheap brushes won't cut it. You must also match the tools to the paint. ie) if using latex paint, don't use a brush made for oil paints.