as somebody with attention difficulties... every college/gradschool lecture i've ever attended has been:

1. pay attention for the first 5-10 minutes. I'm really going to try this time!

2. hear something interesting, and your mind starts wandering

3. uhoh, i have no idea what the lecture is talking about now. i'll just keep daydreaming. don't even think about raisigin your hand to ask a question because it'll reveal that you haven't been listening.

4. go home and read the textbook to figure learn the content