I think that most of us took it seriously, but it was also something of a grind. The lack of enthusiasm was usually due to being in a rough environment and dealing with lots of negative reactions. On days with nice weather, where we were visiting houses and not apartment buildings, it could be pleasant.
I didn't like feeling as if we were annoying people, even though we felt the work was important. So many people knew that when the doorbell rang at 10:30am on a Saturday or Sunday, it was those -bleeping- Jehovah's Witnesses. And they made sure we knew that they were aggravated. The few times we would find someone who would listen at all were nice, but those got fewer and fewer, it seemed.
If I had been given the option to stand next to a magazine rack and smile as people walked past, it would have felt as a bit of a relief. It wouldn't have felt like real preaching, but it would have been less stressful.