Watch the Establishing A Motif online guitar lesson by Jason Loughlin from Blues Connections: Major
A motif is like the main idea of a paragraph. It's a statement that should be clear and concise. You have the rest of the solo expand upon your idea. If you make your idea too complicated, the listener won't be invested immediately. You'll also leave yourself with no room to develop it. These kind of solos tend to run out of steam quickly. We want to take a listener on a journey.