Pencil doesn't keep the width profile

Hi, I'm having an issue in illustrator. 
When I use the pencil tool, and select a line in the variable width profile... and I start to draw.. my pencil changes automatically to the basic line (uniform line ), and doesn't keep the profile I select (example width profile 1)... should I preset something in order to keep the line I choose? (I'm learning in a video course, and the designer chooses the width, a color and starts to paint many lines without loosing the selected width.).. help, thank you.