Passivity can hinder learning. Lectures lack feedback to both the instructor and the student about the students' learning. They encourage one-way communication. Lectures require an effective speaker who can vary tone, pitch, and pace of delivery. Lecturers must be verbally fluent, a skill that is not stressed nor learned in many PhD programs and is, in general, distributed unevenly among people.
Lectures place the burden of organizing and synthesizing content solely on the lecturer.
They are not well suited to higher levels of learning such as application, analysis, and synthesis. Lectures are not well suited to complex, detailed, or abstract material. Lectures assume that all students are learning at the same pace and at the same level of understanding, which is hardly ever true. Lectures do not sustain student attention, which wanes very quickly in one to 25 minutes. Lectures tend to be forgotten quickly.