no one would have attended the lecture if you told truth about the guest speaker

... if you had told ...

Sequence of verb tenses.

Here's a chart to help you understand the sequence of tenses better:

http://grammar.ccc.commnet.edu/grammar/sequence.htm

If I understand correctly, you're stating that nobody would have attended the lecture if you had told the truth about the guest speaker. While it is difficult to determine the exact circumstances and consequences, here's a possible explanation:

1. Assess the reason behind the lack of attendance: Reflect on why the truth about the guest speaker would have deterred people from attending the lecture. Perhaps the speaker's reputation is not favorable, or the topic is considered uninteresting or controversial.

2. Evaluate the impact of the truth: Consider the potential consequences of revealing the truth about the guest speaker. Determine whether it would directly affect the lecture's attendance or if other factors might contribute as well.

3. Consider alternative approaches: Explore alternative methods to attract participants to the lecture. This can involve advertising the topic, emphasizing the speaker's expertise in related subjects, or highlighting the benefits of attending.

4. Communication strategy: Develop a communication strategy that promotes the lecture without compromising truthfulness. Focus on elements that are likely to interest the target audience and create a positive buzz around the event.

5. Address concerns indirectly: If there are valid concerns about the guest speaker, find ways to mitigate them indirectly. For example, you could invite guest speakers who are well-known in the field or include additional activities or networking opportunities during the event to make it more enticing.

It's important to remember that each situation is unique, and the way you navigate it should always be based on ethical considerations and a genuine desire to create a valuable experience for participants.